This article explores and sheds some light on a feature of the Microsoft Business Rules Engine which I consider to be important in understanding the semantics of rules.   This is the use of ‘or’ to create a group of conditions within a rule.   We will see that ‘or’ has a very specific meaning in Microsoft’s rule engine and that this meaning may not be quite what you might have expected.   We will also see how the MS BRE simplifies the model, making rule creation more intuitive than it might otherwise have been, and we will compare and contrast the use of ‘or’ in the Microsoft Business Rule Engine with the use of ‘or’ in a similar Java-based rules engine called Jess.