diff --git a/trytond/exceptions.py b/trytond/exceptions.py
new file mode 100644
index 0000000000..073170c0bd
--- /dev/null
+++ b/trytond/exceptions.py
@@ -0,0 +1,37 @@
+#This file is part of Tryton.  The COPYRIGHT file at the top level of
+#this repository contains the full copyright notices and license terms.
+
+class UserError(Exception):
+
+    def __init__(self, message, description=''):
+        super(UserError, self).__init__('UserError', (message, description))
+        self.message = message
+        self.description = description
+        self.code = 1
+
+
+class UserWarning(Exception):
+
+    def __init__(self, name, message, description=''):
+        super(UserWarning, self).__init__('UserWarning', (name, message,
+                description))
+        self.name = name
+        self.message = message
+        self.description = description
+        self.code = 2
+
+
+class NotLogged(Exception):
+
+    def __init__(self):
+        super(NotLogged, self).__init__('NotLogged')
+        self.code = 3
+
+
+class ConcurrencyException(Exception):
+
+    def __init__(self, message):
+        super(ConcurrencyException, self).__init__('ConcurrencyException',
+            message)
+        self.message = message
+        self.code = 4