diff --git a/registrasion/controllers/invoice.py b/registrasion/controllers/invoice.py
index 264049c8..de401d31 100644
--- a/registrasion/controllers/invoice.py
+++ b/registrasion/controllers/invoice.py
@@ -3,6 +3,7 @@ from django.core.exceptions import ObjectDoesNotExist
 from django.core.exceptions import ValidationError
 from django.db import transaction
 from django.db.models import Sum
+from django.utils import timezone
 
 from registrasion import models as rego
 
@@ -13,6 +14,7 @@ class InvoiceController(object):
 
     def __init__(self, invoice):
         self.invoice = invoice
+        self.update_status()
         self.update_validity()  # Make sure this invoice is up-to-date
 
     @classmethod
@@ -22,21 +24,26 @@ class InvoiceController(object):
         an invoice is generated.'''
 
         try:
-            invoice = rego.Invoice.objects.get(
+            invoice = rego.Invoice.objects.exclude(
+                status=rego.Invoice.STATUS_VOID,
+            ).get(
                 cart=cart,
                 cart_revision=cart.revision,
-                void=False,
             )
         except ObjectDoesNotExist:
             cart_controller = CartController(cart)
             cart_controller.validate_cart()  # Raises ValidationError on fail.
 
-            # Void past invoices for this cart
-            rego.Invoice.objects.filter(cart=cart).update(void=True)
-
+            cls.void_all_invoices(cart)
             invoice = cls._generate(cart)
 
-        return InvoiceController(invoice)
+        return cls(invoice)
+
+    @classmethod
+    def void_all_invoices(cls, cart):
+        invoices = rego.Invoice.objects.filter(cart=cart).all()
+        for invoice in invoices:
+            cls(invoice).void()
 
     @classmethod
     def resolve_discount_value(cls, item):
@@ -60,11 +67,26 @@ class InvoiceController(object):
     @transaction.atomic
     def _generate(cls, cart):
         ''' Generates an invoice for the given cart. '''
+
+        issued = timezone.now()
+        reservation_limit = cart.reservation_duration + cart.time_last_updated
+        # Never generate a due time that is before the issue time
+        due = max(issued, reservation_limit)
+
+        # Get the invoice recipient
+        profile = rego.AttendeeProfileBase.objects.get_subclass(
+            id=cart.user.attendee.attendeeprofilebase.id,
+        )
+        recipient = profile.invoice_recipient()
         invoice = rego.Invoice.objects.create(
             user=cart.user,
             cart=cart,
             cart_revision=cart.revision,
-            value=Decimal()
+            status=rego.Invoice.STATUS_UNPAID,
+            value=Decimal(),
+            issue_time=issued,
+            due_time=due,
+            recipient=recipient,
         )
 
         product_items = rego.ProductItem.objects.filter(cart=cart)
@@ -84,6 +106,7 @@ class InvoiceController(object):
                 description="%s - %s" % (product.category.name, product.name),
                 quantity=item.quantity,
                 price=product.price,
+                product=product,
             )
             invoice_value += line_item.quantity * line_item.price
 
@@ -93,94 +116,162 @@ class InvoiceController(object):
                 description=item.discount.description,
                 quantity=item.quantity,
                 price=cls.resolve_discount_value(item) * -1,
+                product=item.product,
             )
             invoice_value += line_item.quantity * line_item.price
 
         invoice.value = invoice_value
 
-        if invoice.value == 0:
-            invoice.paid = True
-
         invoice.save()
 
         return invoice
 
+    def can_view(self, user=None, access_code=None):
+        ''' Returns true if the accessing user is allowed to view this invoice,
+        or if the given access code matches this invoice's user's access code.
+        '''
+
+        if user == self.invoice.user:
+            return True
+
+        if user.is_staff:
+            return True
+
+        if self.invoice.user.attendee.access_code == access_code:
+            return True
+
+        return False
+
+
+    def _refresh(self):
+        ''' Refreshes the underlying invoice and cart objects. '''
+        self.invoice.refresh_from_db()
+        if self.invoice.cart:
+            self.invoice.cart.refresh_from_db()
+
+    def validate_allowed_to_pay(self):
+        ''' Passes cleanly if we're allowed to pay, otherwise raise
+        a ValidationError. '''
+
+        self._refresh()
+
+        if not self.invoice.is_unpaid:
+            raise ValidationError("You can only pay for unpaid invoices.")
+
+        if not self.invoice.cart:
+            return
+
+        if not self._invoice_matches_cart():
+            raise ValidationError("The registration has been amended since "
+                                  "generating this invoice.")
+
+        CartController(self.invoice.cart).validate_cart()
+
+    def total_payments(self):
+        ''' Returns the total amount paid towards this invoice. '''
+
+        payments = rego.PaymentBase.objects.filter(invoice=self.invoice)
+        total_paid = payments.aggregate(Sum("amount"))["amount__sum"] or 0
+        return total_paid
+
+    def update_status(self):
+        ''' Updates the status of this invoice based upon the total
+        payments.'''
+
+        old_status = self.invoice.status
+        total_paid = self.total_payments()
+        num_payments = rego.PaymentBase.objects.filter(
+            invoice=self.invoice,
+        ).count()
+        remainder = self.invoice.value - total_paid
+
+        if old_status == rego.Invoice.STATUS_UNPAID:
+            # Invoice had an amount owing
+            if remainder <= 0:
+                # Invoice no longer has amount owing
+                self._mark_paid()
+            elif total_paid == 0 and num_payments > 0:
+                # Invoice has multiple payments totalling zero
+                self._mark_void()
+        elif old_status == rego.Invoice.STATUS_PAID:
+            if remainder > 0:
+                # Invoice went from having a remainder of zero or less
+                # to having a positive remainder -- must be a refund
+                self._mark_refunded()
+        elif old_status == rego.Invoice.STATUS_REFUNDED:
+            # Should not ever change from here
+            pass
+        elif old_status == rego.Invoice.STATUS_VOID:
+            # Should not ever change from here
+            pass
+
+    def _mark_paid(self):
+        ''' Marks the invoice as paid, and updates the attached cart if
+        necessary. '''
+        cart = self.invoice.cart
+        if cart:
+            cart.active = False
+            cart.save()
+        self.invoice.status = rego.Invoice.STATUS_PAID
+        self.invoice.save()
+
+    def _mark_refunded(self):
+        ''' Marks the invoice as refunded, and updates the attached cart if
+        necessary. '''
+        cart = self.invoice.cart
+        if cart:
+            cart.active = False
+            cart.released = True
+            cart.save()
+        self.invoice.status = rego.Invoice.STATUS_REFUNDED
+        self.invoice.save()
+
+    def _mark_void(self):
+        ''' Marks the invoice as refunded, and updates the attached cart if
+        necessary. '''
+        self.invoice.status = rego.Invoice.STATUS_VOID
+        self.invoice.save()
+
+    def _invoice_matches_cart(self):
+        ''' Returns true if there is no cart, or if the revision of this
+        invoice matches the current revision of the cart. '''
+        cart = self.invoice.cart
+        if not cart:
+            return True
+
+        return cart.revision == self.invoice.cart_revision
+
     def update_validity(self):
-        ''' Updates the validity of this invoice if the cart it is attached to
-        has updated. '''
-        if self.invoice.cart is not None:
-            if self.invoice.cart.revision != self.invoice.cart_revision:
-                self.void()
+        ''' Voids this invoice if the cart it is attached to has updated. '''
+        if not self._invoice_matches_cart():
+            self.void()
 
     def void(self):
         ''' Voids the invoice if it is valid to do so. '''
-        if self.invoice.paid:
+        if self.invoice.status == rego.Invoice.STATUS_PAID:
             raise ValidationError("Paid invoices cannot be voided, "
                                   "only refunded.")
-        self.invoice.void = True
-        self.invoice.save()
-
-    @transaction.atomic
-    def pay(self, reference, amount):
-        ''' Pays the invoice by the given amount. If the payment
-        equals the total on the invoice, finalise the invoice.
-        (NB should be transactional.)
-        '''
-        if self.invoice.cart:
-            cart = CartController(self.invoice.cart)
-            cart.validate_cart()  # Raises ValidationError if invalid
-
-        if self.invoice.void:
-            raise ValidationError("Void invoices cannot be paid")
-
-        if self.invoice.paid:
-            raise ValidationError("Paid invoices cannot be paid again")
-
-        ''' Adds a payment '''
-        payment = rego.Payment.objects.create(
-            invoice=self.invoice,
-            reference=reference,
-            amount=amount,
-        )
-        payment.save()
-
-        payments = rego.Payment.objects.filter(invoice=self.invoice)
-        agg = payments.aggregate(Sum("amount"))
-        total = agg["amount__sum"]
-
-        if total == self.invoice.value:
-            self.invoice.paid = True
-
-            if self.invoice.cart:
-                cart = self.invoice.cart
-                cart.active = False
-                cart.save()
-
-            self.invoice.save()
+        self._mark_void()
 
     @transaction.atomic
     def refund(self, reference, amount):
-        ''' Refunds the invoice by the given amount. The invoice is
-        marked as unpaid, and the underlying cart is marked as released.
+        ''' Refunds the invoice by the given amount.
+
+        The invoice is marked as refunded, and the underlying cart is marked
+        as released.
+
+        TODO: replace with credit notes work instead.
         '''
 
-        if self.invoice.void:
+        if self.invoice.is_void:
             raise ValidationError("Void invoices cannot be refunded")
 
-        ''' Adds a payment '''
-        payment = rego.Payment.objects.create(
+        # Adds a payment
+        # TODO: replace by creating a credit note instead
+        rego.ManualPayment.objects.create(
             invoice=self.invoice,
             reference=reference,
             amount=0 - amount,
         )
-        payment.save()
 
-        self.invoice.paid = False
-        self.invoice.void = True
-
-        if self.invoice.cart:
-            cart = self.invoice.cart
-            cart.released = True
-            cart.save()
-
-        self.invoice.save()
+        self.update_status()
diff --git a/registrasion/forms.py b/registrasion/forms.py
index 47dacd3d..68c69d36 100644
--- a/registrasion/forms.py
+++ b/registrasion/forms.py
@@ -3,6 +3,13 @@ import models as rego
 from django import forms
 
 
+class ManualPaymentForm(forms.ModelForm):
+
+    class Meta:
+        model = rego.ManualPayment
+        fields = ["reference", "amount"]
+
+
 # Products forms -- none of these have any fields: they are to be subclassed
 # and the fields added as needs be.
 
diff --git a/registrasion/migrations/0013_auto_20160406_2228_squashed_0015_auto_20160406_1942.py b/registrasion/migrations/0013_auto_20160406_2228_squashed_0015_auto_20160406_1942.py
new file mode 100644
index 00000000..e4d88313
--- /dev/null
+++ b/registrasion/migrations/0013_auto_20160406_2228_squashed_0015_auto_20160406_1942.py
@@ -0,0 +1,88 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.2 on 2016-04-07 03:13
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+import django.utils.timezone
+
+
+class Migration(migrations.Migration):
+
+    replaces = [('registrasion', '0013_auto_20160406_2228'), ('registrasion', '0014_auto_20160406_1847'), ('registrasion', '0015_auto_20160406_1942')]
+
+    dependencies = [
+        ('registrasion', '0012_auto_20160406_1212'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='PaymentBase',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('time', models.DateTimeField(default=django.utils.timezone.now)),
+                ('reference', models.CharField(max_length=255)),
+                ('amount', models.DecimalField(decimal_places=2, max_digits=8)),
+            ],
+        ),
+        migrations.RemoveField(
+            model_name='payment',
+            name='invoice',
+        ),
+        migrations.RemoveField(
+            model_name='invoice',
+            name='paid',
+        ),
+        migrations.RemoveField(
+            model_name='invoice',
+            name='void',
+        ),
+        migrations.AddField(
+            model_name='invoice',
+            name='due_time',
+            field=models.DateTimeField(default=django.utils.timezone.now),
+            preserve_default=False,
+        ),
+        migrations.AddField(
+            model_name='invoice',
+            name='issue_time',
+            field=models.DateTimeField(default=django.utils.timezone.now),
+            preserve_default=False,
+        ),
+        migrations.AddField(
+            model_name='invoice',
+            name='recipient',
+            field=models.CharField(default='Lol', max_length=1024),
+            preserve_default=False,
+        ),
+        migrations.AddField(
+            model_name='invoice',
+            name='status',
+            field=models.IntegerField(choices=[(1, 'Unpaid'), (2, 'Paid'), (3, 'Refunded'), (4, 'VOID')], db_index=True),
+        ),
+        migrations.AddField(
+            model_name='lineitem',
+            name='product',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='registrasion.Product'),
+        ),
+        migrations.CreateModel(
+            name='ManualPayment',
+            fields=[
+                ('paymentbase_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='registrasion.PaymentBase')),
+            ],
+            bases=('registrasion.paymentbase',),
+        ),
+        migrations.DeleteModel(
+            name='Payment',
+        ),
+        migrations.AddField(
+            model_name='paymentbase',
+            name='invoice',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='registrasion.Invoice'),
+        ),
+        migrations.AlterField(
+            model_name='invoice',
+            name='cart_revision',
+            field=models.IntegerField(db_index=True, null=True),
+        ),
+    ]
diff --git a/registrasion/migrations/0014_attendee_access_code.py b/registrasion/migrations/0014_attendee_access_code.py
new file mode 100644
index 00000000..a579f47a
--- /dev/null
+++ b/registrasion/migrations/0014_attendee_access_code.py
@@ -0,0 +1,21 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.2 on 2016-04-08 02:20
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import registrasion.util
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('registrasion', '0013_auto_20160406_2228_squashed_0015_auto_20160406_1942'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='attendee',
+            name='access_code',
+            field=models.CharField(default=registrasion.util.generate_access_code, max_length=6, unique=True),
+        ),
+    ]
diff --git a/registrasion/migrations/0015_auto_20160408_0220.py b/registrasion/migrations/0015_auto_20160408_0220.py
new file mode 100644
index 00000000..acdde45f
--- /dev/null
+++ b/registrasion/migrations/0015_auto_20160408_0220.py
@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.2 on 2016-04-08 02:20
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('registrasion', '0014_attendee_access_code'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='attendee',
+            name='access_code',
+            field=models.CharField(max_length=6, unique=True),
+        ),
+    ]
diff --git a/registrasion/migrations/0016_auto_20160408_0234.py b/registrasion/migrations/0016_auto_20160408_0234.py
new file mode 100644
index 00000000..94beb184
--- /dev/null
+++ b/registrasion/migrations/0016_auto_20160408_0234.py
@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.2 on 2016-04-08 02:34
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('registrasion', '0015_auto_20160408_0220'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='attendee',
+            name='access_code',
+            field=models.CharField(db_index=True, max_length=6, unique=True),
+        ),
+    ]
diff --git a/registrasion/models.py b/registrasion/models.py
index 941ebef5..2719dd0e 100644
--- a/registrasion/models.py
+++ b/registrasion/models.py
@@ -1,8 +1,11 @@
 from __future__ import unicode_literals
 
+import util
+
 import datetime
 import itertools
 
+from django.core.exceptions import ObjectDoesNotExist
 from django.core.exceptions import ValidationError
 from django.contrib.auth.models import User
 from django.db import models
@@ -26,16 +29,25 @@ class Attendee(models.Model):
     def get_instance(user):
         ''' Returns the instance of attendee for the given user, or creates
         a new one. '''
-        attendees = Attendee.objects.filter(user=user)
-        if len(attendees) > 0:
-            return attendees[0]
-        else:
-            attendee = Attendee(user=user)
-            attendee.save()
-            return attendee
+        try:
+            return Attendee.objects.get(user=user)
+        except ObjectDoesNotExist:
+            return Attendee.objects.create(user=user)
+
+    def save(self, *a, **k):
+        while not self.access_code:
+            access_code = util.generate_access_code()
+            if Attendee.objects.filter(access_code=access_code).count() == 0:
+                self.access_code = access_code
+        return super(Attendee, self).save(*a, **k)
 
     user = models.OneToOneField(User, on_delete=models.CASCADE)
     # Badge/profile is linked
+    access_code = models.CharField(
+        max_length=6,
+        unique=True,
+        db_index=True,
+    )
     completed_registration = models.BooleanField(default=False)
     highest_complete_category = models.IntegerField(default=0)
 
@@ -54,6 +66,19 @@ class AttendeeProfileBase(models.Model):
         speaker profile. If it's None, that functionality is disabled. '''
         return None
 
+    def invoice_recipient(self):
+        ''' Returns a representation of this attendee profile for the purpose
+        of rendering to an invoice. Override in subclasses. '''
+
+        # Manual dispatch to subclass. Fleh.
+        slf = AttendeeProfileBase.objects.get_subclass(id=self.id)
+        # Actually compare the functions.
+        if type(slf).invoice_recipient != type(self).invoice_recipient:
+            return type(slf).invoice_recipient(slf)
+
+        # Return a default
+        return slf.attendee.user.username
+
     attendee = models.OneToOneField(Attendee, on_delete=models.CASCADE)
 
 
@@ -533,6 +558,18 @@ class Invoice(models.Model):
     ''' An invoice. Invoices can be automatically generated when checking out
     a Cart, in which case, it is attached to a given revision of a Cart. '''
 
+    STATUS_UNPAID = 1
+    STATUS_PAID = 2
+    STATUS_REFUNDED = 3
+    STATUS_VOID = 4
+
+    STATUS_TYPES = [
+        (STATUS_UNPAID, _("Unpaid")),
+        (STATUS_PAID, _("Paid")),
+        (STATUS_REFUNDED, _("Refunded")),
+        (STATUS_VOID, _("VOID")),
+    ]
+
     def __str__(self):
         return "Invoice #%d" % self.id
 
@@ -541,13 +578,37 @@ class Invoice(models.Model):
             raise ValidationError(
                 "If this is a cart invoice, it must have a revision")
 
+    @property
+    def is_unpaid(self):
+        return self.status == self.STATUS_UNPAID
+
+    @property
+    def is_void(self):
+        return self.status == self.STATUS_VOID
+
+    @property
+    def is_paid(self):
+        return self.status == self.STATUS_PAID
+
+    @property
+    def is_refunded(self):
+        return self.status == self.STATUS_REFUNDED
+
     # Invoice Number
     user = models.ForeignKey(User)
     cart = models.ForeignKey(Cart, null=True)
-    cart_revision = models.IntegerField(null=True)
+    cart_revision = models.IntegerField(
+        null=True,
+        db_index=True,
+    )
     # Line Items (foreign key)
-    void = models.BooleanField(default=False)
-    paid = models.BooleanField(default=False)
+    status = models.IntegerField(
+        choices=STATUS_TYPES,
+        db_index=True,
+    )
+    recipient = models.CharField(max_length=1024)
+    issue_time = models.DateTimeField()
+    due_time = models.DateTimeField()
     value = models.DecimalField(max_digits=8, decimal_places=2)
 
 
@@ -565,17 +626,25 @@ class LineItem(models.Model):
     description = models.CharField(max_length=255)
     quantity = models.PositiveIntegerField()
     price = models.DecimalField(max_digits=8, decimal_places=2)
+    product = models.ForeignKey(Product, null=True, blank=True)
 
 
 @python_2_unicode_compatible
-class Payment(models.Model):
-    ''' A payment for an invoice. Each invoice can have multiple payments
-    attached to it.'''
+class PaymentBase(models.Model):
+    ''' The base payment type for invoices. Payment apps should subclass this
+    class to handle implementation-specific issues. '''
+
+    objects = InheritanceManager()
 
     def __str__(self):
         return "Payment: ref=%s amount=%s" % (self.reference, self.amount)
 
     invoice = models.ForeignKey(Invoice)
     time = models.DateTimeField(default=timezone.now)
-    reference = models.CharField(max_length=64)
+    reference = models.CharField(max_length=255)
     amount = models.DecimalField(max_digits=8, decimal_places=2)
+
+
+class ManualPayment(PaymentBase):
+    ''' Payments that are manually entered by staff. '''
+    pass
diff --git a/registrasion/tests/cart_controller_helper.py b/registrasion/tests/controller_helpers.py
similarity index 63%
rename from registrasion/tests/cart_controller_helper.py
rename to registrasion/tests/controller_helpers.py
index 9e4191f0..476351dd 100644
--- a/registrasion/tests/cart_controller_helper.py
+++ b/registrasion/tests/controller_helpers.py
@@ -1,7 +1,9 @@
 from registrasion.controllers.cart import CartController
+from registrasion.controllers.invoice import InvoiceController
 from registrasion import models as rego
 
 from django.core.exceptions import ObjectDoesNotExist
+from django.core.exceptions import ValidationError
 
 
 class TestingCartController(CartController):
@@ -28,3 +30,21 @@ class TestingCartController(CartController):
     def next_cart(self):
         self.cart.active = False
         self.cart.save()
+
+
+class TestingInvoiceController(InvoiceController):
+
+    def pay(self, reference, amount):
+        ''' Testing method for simulating an invoice paymenht by the given
+        amount. '''
+
+        self.validate_allowed_to_pay()
+
+        ''' Adds a payment '''
+        payment = rego.ManualPayment.objects.create(
+            invoice=self.invoice,
+            reference=reference,
+            amount=amount,
+        )
+
+        self.update_status()
diff --git a/registrasion/tests/test_cart.py b/registrasion/tests/test_cart.py
index d47d659e..f8a82c21 100644
--- a/registrasion/tests/test_cart.py
+++ b/registrasion/tests/test_cart.py
@@ -10,7 +10,7 @@ from django.test import TestCase
 from registrasion import models as rego
 from registrasion.controllers.product import ProductController
 
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from patch_datetime import SetTimeMixin
 
 UTC = pytz.timezone('UTC')
@@ -23,6 +23,9 @@ class RegistrationCartTestCase(SetTimeMixin, TestCase):
 
     @classmethod
     def setUpTestData(cls):
+
+        super(RegistrationCartTestCase, cls).setUpTestData()
+
         cls.USER_1 = User.objects.create_user(
             username='testuser',
             email='test@example.com',
@@ -33,6 +36,15 @@ class RegistrationCartTestCase(SetTimeMixin, TestCase):
             email='test2@example.com',
             password='top_secret')
 
+        attendee1 = rego.Attendee.get_instance(cls.USER_1)
+        attendee1.save()
+        profile1 = rego.AttendeeProfileBase.objects.create(attendee=attendee1)
+        profile1.save()
+        attendee2 = rego.Attendee.get_instance(cls.USER_2)
+        attendee2.save()
+        profile2 = rego.AttendeeProfileBase.objects.create(attendee=attendee2)
+        profile2.save()
+
         cls.RESERVATION = datetime.timedelta(hours=1)
 
         cls.categories = []
@@ -136,6 +148,10 @@ class RegistrationCartTestCase(SetTimeMixin, TestCase):
         voucher.save()
         return voucher
 
+    @classmethod
+    def reget(cls, object):
+        return type(object).objects.get(id=object.id)
+
 
 class BasicCartTests(RegistrationCartTestCase):
 
diff --git a/registrasion/tests/test_ceilings.py b/registrasion/tests/test_ceilings.py
index f8481fea..c5664481 100644
--- a/registrasion/tests/test_ceilings.py
+++ b/registrasion/tests/test_ceilings.py
@@ -3,7 +3,7 @@ import pytz
 
 from django.core.exceptions import ValidationError
 
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from test_cart import RegistrationCartTestCase
 
 from registrasion import models as rego
diff --git a/registrasion/tests/test_discount.py b/registrasion/tests/test_discount.py
index fb35330e..e9105378 100644
--- a/registrasion/tests/test_discount.py
+++ b/registrasion/tests/test_discount.py
@@ -4,7 +4,8 @@ from decimal import Decimal
 
 from registrasion import models as rego
 from registrasion.controllers import discount
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
+from controller_helpers import TestingInvoiceController
 
 from test_cart import RegistrationCartTestCase
 
diff --git a/registrasion/tests/test_enabling_condition.py b/registrasion/tests/test_enabling_condition.py
index 5d0e410c..d977cc5c 100644
--- a/registrasion/tests/test_enabling_condition.py
+++ b/registrasion/tests/test_enabling_condition.py
@@ -4,7 +4,7 @@ from django.core.exceptions import ValidationError
 
 from registrasion import models as rego
 from registrasion.controllers.category import CategoryController
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from registrasion.controllers.product import ProductController
 
 from test_cart import RegistrationCartTestCase
diff --git a/registrasion/tests/test_invoice.py b/registrasion/tests/test_invoice.py
index 19332392..b121bfa1 100644
--- a/registrasion/tests/test_invoice.py
+++ b/registrasion/tests/test_invoice.py
@@ -5,8 +5,8 @@ from decimal import Decimal
 from django.core.exceptions import ValidationError
 
 from registrasion import models as rego
-from cart_controller_helper import TestingCartController
-from registrasion.controllers.invoice import InvoiceController
+from controller_helpers import TestingCartController
+from controller_helpers import TestingInvoiceController
 
 from test_cart import RegistrationCartTestCase
 
@@ -20,7 +20,7 @@ class InvoiceTestCase(RegistrationCartTestCase):
 
         # Should be able to create an invoice after the product is added
         current_cart.add_to_cart(self.PROD_1, 1)
-        invoice_1 = InvoiceController.for_cart(current_cart.cart)
+        invoice_1 = TestingInvoiceController.for_cart(current_cart.cart)
         # That invoice should have a single line item
         line_items = rego.LineItem.objects.filter(invoice=invoice_1.invoice)
         self.assertEqual(1, len(line_items))
@@ -29,14 +29,14 @@ class InvoiceTestCase(RegistrationCartTestCase):
 
         # Adding item to cart should produce a new invoice
         current_cart.add_to_cart(self.PROD_2, 1)
-        invoice_2 = InvoiceController.for_cart(current_cart.cart)
+        invoice_2 = TestingInvoiceController.for_cart(current_cart.cart)
         self.assertNotEqual(invoice_1.invoice, invoice_2.invoice)
 
         # The old invoice should automatically be voided
         invoice_1_new = rego.Invoice.objects.get(pk=invoice_1.invoice.id)
         invoice_2_new = rego.Invoice.objects.get(pk=invoice_2.invoice.id)
-        self.assertTrue(invoice_1_new.void)
-        self.assertFalse(invoice_2_new.void)
+        self.assertTrue(invoice_1_new.is_void)
+        self.assertFalse(invoice_2_new.is_void)
 
         # Invoice should have two line items
         line_items = rego.LineItem.objects.filter(invoice=invoice_2.invoice)
@@ -58,17 +58,17 @@ class InvoiceTestCase(RegistrationCartTestCase):
 
         # Now try to invoice the first user
         with self.assertRaises(ValidationError):
-            InvoiceController.for_cart(current_cart.cart)
+            TestingInvoiceController.for_cart(current_cart.cart)
 
     def test_paying_invoice_makes_new_cart(self):
         current_cart = TestingCartController.for_user(self.USER_1)
         current_cart.add_to_cart(self.PROD_1, 1)
 
-        invoice = InvoiceController.for_cart(current_cart.cart)
+        invoice = TestingInvoiceController.for_cart(current_cart.cart)
         invoice.pay("A payment!", invoice.invoice.value)
 
         # This payment is for the correct amount invoice should be paid.
-        self.assertTrue(invoice.invoice.paid)
+        self.assertTrue(invoice.invoice.is_paid)
 
         # Cart should not be active
         self.assertFalse(invoice.invoice.cart.active)
@@ -99,7 +99,7 @@ class InvoiceTestCase(RegistrationCartTestCase):
 
         # Should be able to create an invoice after the product is added
         current_cart.add_to_cart(self.PROD_1, 1)
-        invoice_1 = InvoiceController.for_cart(current_cart.cart)
+        invoice_1 = TestingInvoiceController.for_cart(current_cart.cart)
 
         # That invoice should have two line items
         line_items = rego.LineItem.objects.filter(invoice=invoice_1.invoice)
@@ -131,43 +131,43 @@ class InvoiceTestCase(RegistrationCartTestCase):
 
         # Should be able to create an invoice after the product is added
         current_cart.add_to_cart(self.PROD_1, 1)
-        invoice_1 = InvoiceController.for_cart(current_cart.cart)
+        invoice_1 = TestingInvoiceController.for_cart(current_cart.cart)
 
-        self.assertTrue(invoice_1.invoice.paid)
+        self.assertTrue(invoice_1.invoice.is_paid)
 
     def test_invoice_voids_self_if_cart_is_invalid(self):
         current_cart = TestingCartController.for_user(self.USER_1)
 
         # Should be able to create an invoice after the product is added
         current_cart.add_to_cart(self.PROD_1, 1)
-        invoice_1 = InvoiceController.for_cart(current_cart.cart)
+        invoice_1 = TestingInvoiceController.for_cart(current_cart.cart)
 
-        self.assertFalse(invoice_1.invoice.void)
+        self.assertFalse(invoice_1.invoice.is_void)
 
         # Adding item to cart should produce a new invoice
         current_cart.add_to_cart(self.PROD_2, 1)
-        invoice_2 = InvoiceController.for_cart(current_cart.cart)
+        invoice_2 = TestingInvoiceController.for_cart(current_cart.cart)
         self.assertNotEqual(invoice_1.invoice, invoice_2.invoice)
 
         # Viewing invoice_1's invoice should show it as void
-        invoice_1_new = InvoiceController(invoice_1.invoice)
-        self.assertTrue(invoice_1_new.invoice.void)
+        invoice_1_new = TestingInvoiceController(invoice_1.invoice)
+        self.assertTrue(invoice_1_new.invoice.is_void)
 
         # Viewing invoice_2's invoice should *not* show it as void
-        invoice_2_new = InvoiceController(invoice_2.invoice)
-        self.assertFalse(invoice_2_new.invoice.void)
+        invoice_2_new = TestingInvoiceController(invoice_2.invoice)
+        self.assertFalse(invoice_2_new.invoice.is_void)
 
     def test_voiding_invoice_creates_new_invoice(self):
         current_cart = TestingCartController.for_user(self.USER_1)
 
         # Should be able to create an invoice after the product is added
         current_cart.add_to_cart(self.PROD_1, 1)
-        invoice_1 = InvoiceController.for_cart(current_cart.cart)
+        invoice_1 = TestingInvoiceController.for_cart(current_cart.cart)
 
-        self.assertFalse(invoice_1.invoice.void)
+        self.assertFalse(invoice_1.invoice.is_void)
         invoice_1.void()
 
-        invoice_2 = InvoiceController.for_cart(current_cart.cart)
+        invoice_2 = TestingInvoiceController.for_cart(current_cart.cart)
         self.assertNotEqual(invoice_1.invoice, invoice_2.invoice)
 
     def test_cannot_pay_void_invoice(self):
@@ -175,19 +175,19 @@ class InvoiceTestCase(RegistrationCartTestCase):
 
         # Should be able to create an invoice after the product is added
         current_cart.add_to_cart(self.PROD_1, 1)
-        invoice_1 = InvoiceController.for_cart(current_cart.cart)
+        invoice_1 = TestingInvoiceController.for_cart(current_cart.cart)
 
         invoice_1.void()
 
         with self.assertRaises(ValidationError):
-            invoice_1.pay("Reference", invoice_1.invoice.value)
+            invoice_1.validate_allowed_to_pay()
 
     def test_cannot_void_paid_invoice(self):
         current_cart = TestingCartController.for_user(self.USER_1)
 
         # Should be able to create an invoice after the product is added
         current_cart.add_to_cart(self.PROD_1, 1)
-        invoice_1 = InvoiceController.for_cart(current_cart.cart)
+        invoice_1 = TestingInvoiceController.for_cart(current_cart.cart)
 
         invoice_1.pay("Reference", invoice_1.invoice.value)
 
@@ -197,4 +197,24 @@ class InvoiceTestCase(RegistrationCartTestCase):
     def test_cannot_generate_blank_invoice(self):
         current_cart = TestingCartController.for_user(self.USER_1)
         with self.assertRaises(ValidationError):
-            InvoiceController.for_cart(current_cart.cart)
+            invoice_1 = TestingInvoiceController.for_cart(current_cart.cart)
+
+    def test_cannot_pay_implicitly_void_invoice(self):
+        cart = TestingCartController.for_user(self.USER_1)
+        cart.add_to_cart(self.PROD_1, 1)
+        invoice = TestingInvoiceController.for_cart(self.reget(cart.cart))
+
+        # Implicitly void the invoice
+        cart.add_to_cart(self.PROD_1, 1)
+
+        with self.assertRaises(ValidationError):
+            invoice.validate_allowed_to_pay()
+
+
+
+    # TODO: test partially paid invoice cannot be void until payments
+    # are refunded
+
+    # TODO: test overpaid invoice results in credit note
+
+    # TODO: test credit note generation more generally
diff --git a/registrasion/tests/test_refund.py b/registrasion/tests/test_refund.py
index bde25929..35457749 100644
--- a/registrasion/tests/test_refund.py
+++ b/registrasion/tests/test_refund.py
@@ -1,7 +1,7 @@
 import pytz
 
-from cart_controller_helper import TestingCartController
-from registrasion.controllers.invoice import InvoiceController
+from controller_helpers import TestingCartController
+from controller_helpers import TestingInvoiceController
 
 from test_cart import RegistrationCartTestCase
 
@@ -15,14 +15,16 @@ class RefundTestCase(RegistrationCartTestCase):
 
         # Should be able to create an invoice after the product is added
         current_cart.add_to_cart(self.PROD_1, 1)
-        invoice = InvoiceController.for_cart(current_cart.cart)
+        invoice = TestingInvoiceController.for_cart(current_cart.cart)
 
         invoice.pay("A Payment!", invoice.invoice.value)
-        self.assertFalse(invoice.invoice.void)
-        self.assertTrue(invoice.invoice.paid)
+        self.assertFalse(invoice.invoice.is_void)
+        self.assertTrue(invoice.invoice.is_paid)
+        self.assertFalse(invoice.invoice.is_refunded)
         self.assertFalse(invoice.invoice.cart.released)
 
         invoice.refund("A Refund!", invoice.invoice.value)
-        self.assertTrue(invoice.invoice.void)
-        self.assertFalse(invoice.invoice.paid)
+        self.assertFalse(invoice.invoice.is_void)
+        self.assertFalse(invoice.invoice.is_paid)
+        self.assertTrue(invoice.invoice.is_refunded)
         self.assertTrue(invoice.invoice.cart.released)
diff --git a/registrasion/tests/test_voucher.py b/registrasion/tests/test_voucher.py
index a8bc6b00..be598206 100644
--- a/registrasion/tests/test_voucher.py
+++ b/registrasion/tests/test_voucher.py
@@ -6,8 +6,8 @@ from django.core.exceptions import ValidationError
 from django.db import IntegrityError
 
 from registrasion import models as rego
-from cart_controller_helper import TestingCartController
-from registrasion.controllers.invoice import InvoiceController
+from controller_helpers import TestingCartController
+from controller_helpers import TestingInvoiceController
 
 from test_cart import RegistrationCartTestCase
 
@@ -140,8 +140,8 @@ class VoucherTestCases(RegistrationCartTestCase):
         current_cart.apply_voucher(voucher.code)
         current_cart.add_to_cart(self.PROD_1, 1)
 
-        inv = InvoiceController.for_cart(current_cart.cart)
-        if not inv.invoice.paid:
+        inv = TestingInvoiceController.for_cart(current_cart.cart)
+        if not inv.invoice.is_paid:
             inv.pay("Hello!", inv.invoice.value)
 
         current_cart = TestingCartController.for_user(self.USER_1)
diff --git a/registrasion/urls.py b/registrasion/urls.py
index 0620dafb..0949e4b4 100644
--- a/registrasion/urls.py
+++ b/registrasion/urls.py
@@ -1,3 +1,5 @@
+import views
+
 from django.conf.urls import url, patterns
 
 urlpatterns = patterns(
@@ -5,7 +7,11 @@ urlpatterns = patterns(
     url(r"^category/([0-9]+)$", "product_category", name="product_category"),
     url(r"^checkout$", "checkout", name="checkout"),
     url(r"^invoice/([0-9]+)$", "invoice", name="invoice"),
-    url(r"^invoice/([0-9]+)/pay$", "pay_invoice", name="pay_invoice"),
+    url(r"^invoice/([0-9]+)/([A-Z0-9]+)$", views.invoice, name="invoice"),
+    url(r"^invoice/([0-9]+)/manual_payment$",
+        views.manual_payment, name="manual_payment"),
+    url(r"^invoice_access/([A-Z0-9]+)$", views.invoice_access,
+        name="invoice_access"),
     url(r"^profile$", "edit_profile", name="attendee_edit"),
     url(r"^register$", "guided_registration", name="guided_registration"),
     url(r"^register/([0-9]+)$", "guided_registration",
diff --git a/registrasion/util.py b/registrasion/util.py
new file mode 100644
index 00000000..fb97d1d5
--- /dev/null
+++ b/registrasion/util.py
@@ -0,0 +1,15 @@
+import string
+
+from django.utils.crypto import get_random_string
+
+def generate_access_code():
+    ''' Generates an access code for users' payments as well as their
+    fulfilment code for check-in.
+    The access code will 4 characters long, which allows for 1,500,625
+    unique codes, which really should be enough for anyone. '''
+
+    length = 4
+    # all upper-case letters + digits 1-9 (no 0 vs O confusion)
+    chars = string.uppercase + string.digits[1:]
+    # 4 chars => 35 ** 4 = 1500625 (should be enough for anyone)
+    return get_random_string(length=length, allowed_chars=chars)
diff --git a/registrasion/views.py b/registrasion/views.py
index b3f9212d..251f0fba 100644
--- a/registrasion/views.py
+++ b/registrasion/views.py
@@ -16,6 +16,7 @@ from django.contrib import messages
 from django.core.exceptions import ObjectDoesNotExist
 from django.core.exceptions import ValidationError
 from django.http import Http404
+from django.shortcuts import get_object_or_404
 from django.shortcuts import redirect
 from django.shortcuts import render
 
@@ -423,18 +424,41 @@ def checkout_errors(request, errors):
     return render(request, "registrasion/checkout_errors.html", data)
 
 
-@login_required
-def invoice(request, invoice_id):
-    ''' Displays an invoice for a given invoice id. '''
+def invoice_access(request, access_code):
+    ''' Redirects to the first unpaid invoice for the attendee that matches
+    the given access code, if any. '''
+
+    invoices = rego.Invoice.objects.filter(
+        user__attendee__access_code=access_code,
+        status=rego.Invoice.STATUS_UNPAID,
+    ).order_by("issue_time")
+
+    if not invoices:
+        raise Http404()
+
+    invoice = invoices[0]
+
+    return redirect("invoice", invoice.id, access_code)
+
+
+def invoice(request, invoice_id, access_code=None):
+    ''' Displays an invoice for a given invoice id.
+    This view is not authenticated, but it will only allow access to either:
+    the user the invoice belongs to; staff; or a request made with the correct
+    access code.
+    '''
 
     invoice_id = int(invoice_id)
     inv = rego.Invoice.objects.get(pk=invoice_id)
 
-    if request.user != inv.cart.user and not request.user.is_staff:
-        raise Http404()
-
     current_invoice = InvoiceController(inv)
 
+    if not current_invoice.can_view(
+            user=request.user,
+            access_code=access_code,
+        ):
+        raise Http404()
+
     data = {
         "invoice": current_invoice.invoice,
     }
@@ -443,15 +467,32 @@ def invoice(request, invoice_id):
 
 
 @login_required
-def pay_invoice(request, invoice_id):
-    ''' Marks the invoice with the given invoice id as paid.
-    WORK IN PROGRESS FUNCTION. Must be replaced with real payment workflow.
+def manual_payment(request, invoice_id):
+    ''' Allows staff to make manual payments or refunds on an invoice.'''
+
+    FORM_PREFIX = "manual_payment"
+
+    if not request.user.is_staff:
+        raise Http404()
 
-    '''
     invoice_id = int(invoice_id)
-    inv = rego.Invoice.objects.get(pk=invoice_id)
+    inv = get_object_or_404(rego.Invoice, pk=invoice_id)
     current_invoice = InvoiceController(inv)
-    if not current_invoice.invoice.paid and not current_invoice.invoice.void:
-        current_invoice.pay("Demo invoice payment", inv.value)
 
-    return redirect("invoice", current_invoice.invoice.id)
+    form = forms.ManualPaymentForm(
+        request.POST or None,
+        prefix=FORM_PREFIX,
+    )
+
+    if request.POST and form.is_valid():
+        form.instance.invoice = inv
+        form.save()
+        current_invoice.update_status()
+        form = forms.ManualPaymentForm(prefix=FORM_PREFIX)
+
+    data = {
+        "invoice": inv,
+        "form": form,
+    }
+
+    return render(request, "registrasion/manual_payment.html", data)