diff --git a/commerce/README.txt b/commerce/README.txt
index 37d3dd1..9c38be5 100644
--- a/commerce/README.txt
+++ b/commerce/README.txt
@@ -115,7 +115,8 @@ Orders
 
 The items in a shopping cart may be included in an order.
 
-  >>> ord001 = manager.orders.create(u'001', shop=shop1, customer=c001)
+  >>> orderId = shop1.getNewOrderId()
+  >>> ord001 = manager.orders.create(orderId, shop=shop1, customer=c001)
 
   >>> for item in orderItems.getCart(c001):
   ...     item.setOrder(ord001)
diff --git a/commerce/interfaces.py b/commerce/interfaces.py
index c31a223..a4efd6f 100644
--- a/commerce/interfaces.py
+++ b/commerce/interfaces.py
@@ -76,6 +76,13 @@ class IShop(Interface):
             description=_(u'A medium-length description.'),
             default=u'',
             required=False)
+    orderNumber = schema.Int(
+            title=_(u'Order Number'),
+            description=_(u'The number used for the order identifier of '
+                          u'last order created. This will in turn be used '
+                          u'for creating the next order identifier.'),
+            default=0,
+            required=False)
 
     products = Attribute(u'The products available in this shop.')
     categories = Attribute(u'The product categories provided by this shop.')
@@ -85,6 +92,10 @@ class IShop(Interface):
                     u'this shop.')
     customers = Attribute(u'The customers registered for this shop.')
 
+    def getNewOrderId():
+        """ Create a new order identifier.
+        """
+
 
 # manufacturers and suppliers
 
diff --git a/commerce/shop.py b/commerce/shop.py
index 3290916..98afa61 100644
--- a/commerce/shop.py
+++ b/commerce/shop.py
@@ -1,5 +1,5 @@
 #
-#  Copyright (c) 2008 Helmut Merz helmutm@cy55.de
+#  Copyright (c) 2009 Helmut Merz helmutm@cy55.de
 #
 #  This program is free software; you can redistribute it and/or modify
 #  it under the terms of the GNU General Public License as published by
@@ -39,3 +39,10 @@ class Shop(BaseObject):
         self.title = title or u'Shop'
         self.products = self.collection(self, 'shops')
         self.customers = self.collection(self, 'shops')
+        self.orderNumber = 0
+
+    def getNewOrderId(self):
+        last = self.orderNumber or 0
+        num = last + 1
+        self.orderNumber = num
+        return '%05i' % num