diff --git a/docs/source/interface.rst b/docs/source/interface.rst
index e48f900634ab6bb7d78bf6c48794aab4d4b020fc..74881dc4933192477b16e4a471603b69d27312db 100644
--- a/docs/source/interface.rst
+++ b/docs/source/interface.rst
@@ -10,41 +10,41 @@ SecureAccessTokenAuthorizer publishes an HTTP-based interface inside the main Ta
 ``PUT /storage-plugins/privatestorageio-satauthz-v1/payment-reference-number``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-This endpoint allows an external agent which has submitted a payment to cause the plugin to redeem the payment reference for tokens.
+This endpoint allows an external agent which has submitted a payment to cause the plugin to redeem the voucher for tokens.
 The request body for this endpoint must have the ``application/json`` content-type.
-The request body contains a simple json object containing the payment reference number::
+The request body contains a simple json object containing the voucher::
 
-  {"payment-reference-number": "<payment reference number>"}
+  {"payment-reference-number": "<voucher>"}
 
-The endpoint responds to such a request with an **OK** HTTP response code if the payment reference number is accepted for processing.
-If the payment reference number cannot be accepted at the time of the request then the response code will be anything other than **OK**.
+The endpoint responds to such a request with an **OK** HTTP response code if the voucher is accepted for processing.
+If the voucher cannot be accepted at the time of the request then the response code will be anything other than **OK**.
 
 If the response is **OK** then a repeated request with the same body will have no effect.
 If the response is not **OK** then a repeated request with the same body will try to accept the number again.
 
-``GET /storage-plugins/privatestorageio-satauthz-v1/payment-reference-number/<payment reference number>``
+``GET /storage-plugins/privatestorageio-satauthz-v1/payment-reference-number/<voucher>``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-This endpoint allows an external agent to monitor the status of the redemption of a payment reference number.
+This endpoint allows an external agent to monitor the status of the redemption of a voucher.
 This endpoint accepts no request body.
 
-If the payment reference number is not known then the response is **NOT FOUND**.
-For any payment reference number which has previously been submitted,
+If the voucher is not known then the response is **NOT FOUND**.
+For any voucher which has previously been submitted,
 the response is **OK** with an ``application/json`` content-type response body like::
 
   {"value": <string>}
 
-The ``value`` property merely indicates the payment reference number which was requested.
+The ``value`` property merely indicates the voucher which was requested.
 Further properties will be added to this response in the near future.
 
 ``GET /storage-plugins/privatestorageio-satauthz-v1/payment-reference-number``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-This endpoint allows an external agent to retrieve the status of all payment reference numbers.
+This endpoint allows an external agent to retrieve the status of all vouchers.
 This endpoint accepts no request body.
 
 The response is **OK** with ``application/json`` content-type response body like::
 
-  {"payment-reference-numbers": [<payment reference status object>, ...]}
+  {"payment-reference-numbers": [<voucher status object>, ...]}
 
 The elements of the list are objects like the one returned by issuing a **GET** to a child of this collection resource.
diff --git a/src/_secureaccesstokenauthorizer/resource.py b/src/_secureaccesstokenauthorizer/resource.py
index f1e59d8e9f4752ccb7b31c8653570dc50d18d347..8a9c2154fe6212e3963b8a085010ce7268f1f058 100644
--- a/src/_secureaccesstokenauthorizer/resource.py
+++ b/src/_secureaccesstokenauthorizer/resource.py
@@ -79,11 +79,10 @@ def from_configuration(node_config, store=None):
 
 class _PaymentReferenceNumberCollection(Resource):
     """
-    This class implements redemption of payment reference numbers.  Users
-    **PUT** such numbers to this resource which delegates redemption
-    responsibilities to the redemption controller.  Child resources of this
-    resource can also be retrieved to monitor the status of previously
-    submitted vouchers.
+    This class implements redemption of vouchers.  Users **PUT** such numbers
+    to this resource which delegates redemption responsibilities to the
+    redemption controller.  Child resources of this resource can also be
+    retrieved to monitor the status of previously submitted vouchers.
     """
     def __init__(self, store, controller):
         self._store = store
@@ -136,7 +135,7 @@ def is_syntactic_prn(prn):
     :param prn: A candidate object to inspect.
 
     :return bool: ``True`` if and only if ``prn`` is a unicode string
-        containing a syntactically valid payment reference number.  This says
+        containing a syntactically valid voucher.  This says
         **nothing** about the validity of the represented voucher itself.  A
         ``True`` result only means the unicode string can be **interpreted**
         as a voucher.
diff --git a/src/_secureaccesstokenauthorizer/tests/strategies.py b/src/_secureaccesstokenauthorizer/tests/strategies.py
index 4af061defb0f2d34a3912078e55dfd76e580d205..ad9b2a47d905d32d682e3300f2268819485b18d3 100644
--- a/src/_secureaccesstokenauthorizer/tests/strategies.py
+++ b/src/_secureaccesstokenauthorizer/tests/strategies.py
@@ -163,7 +163,7 @@ def client_configurations():
 
 def payment_reference_numbers():
     """
-    Build unicode strings in the format of payment reference numbers.
+    Build unicode strings in the format of vouchers.
     """
     return binary(
         min_size=32,
diff --git a/src/_secureaccesstokenauthorizer/tests/test_client_resource.py b/src/_secureaccesstokenauthorizer/tests/test_client_resource.py
index 176d6ce0a09625d06dcfa46ce1db37a9d1d92041..6eb2f7227b2bac8bf3654e41533e584788d24127 100644
--- a/src/_secureaccesstokenauthorizer/tests/test_client_resource.py
+++ b/src/_secureaccesstokenauthorizer/tests/test_client_resource.py
@@ -138,7 +138,7 @@ def is_not_json(bytestring):
 
 def not_payment_reference_numbers():
     """
-    Builds unicode strings which are not legal payment reference numbers.
+    Builds unicode strings which are not legal vouchers.
     """
     return one_of(
         text().filter(
@@ -210,7 +210,7 @@ class PaymentReferenceNumberTests(TestCase):
     """
     Tests relating to ``/payment-reference-number`` as implemented by the
     ``_secureaccesstokenauthorizer.resource`` module and its handling of
-    payment reference numbers.
+    vouchers.
     """
     def setUp(self):
         super(PaymentReferenceNumberTests, self).setUp()
@@ -406,7 +406,7 @@ class PaymentReferenceNumberTests(TestCase):
     def test_list_prns(self, get_config, prns):
         """
         A ``GET`` to the ``PaymentReferenceNumberCollection`` itself returns a
-        list of existing payment reference numbers.
+        list of existing vouchers.
         """
         # Hypothesis causes our test case instances to be re-used many times
         # between setUp and tearDown.  Avoid re-using the same temporary
diff --git a/src/_secureaccesstokenauthorizer/tests/test_model.py b/src/_secureaccesstokenauthorizer/tests/test_model.py
index 3ef54d46d16e960fc2728f2abf46309bf1c49fc9..052f5e6fd5f0e2341ba6a28d2eefcbe9d3747b44 100644
--- a/src/_secureaccesstokenauthorizer/tests/test_model.py
+++ b/src/_secureaccesstokenauthorizer/tests/test_model.py
@@ -91,7 +91,7 @@ class PaymentReferenceStoreTests(TestCase):
     def test_get_missing(self, get_config, prn):
         """
         ``PaymentReferenceStore.get`` raises ``KeyError`` when called with a
-        payment reference number not previously added to the store.
+        voucher not previously added to the store.
         """
         tempdir = self.useFixture(TempDir())
         config = get_config(tempdir.join(b"node"), b"tub.port")
@@ -153,8 +153,7 @@ class PaymentReferenceStoreTests(TestCase):
     def test_list(self, get_config, prns):
         """
         ``PaymentReferenceStore.list`` returns a ``list`` containing a
-        ``PaymentReference`` object for each payment reference number
-        previously added.
+        ``PaymentReference`` object for each voucher previously added.
         """
         tempdir = self.useFixture(TempDir())
         nodedir = tempdir.join(b"node")