The paper reviews major Economics textbooks used in the UK from the point of view of their use of rationality as a teaching tool. The textbooks vary widely in their explicit analysis of rationality from finding it important to totally ignoring it. When textbooks do use the concept as part of their analysis, the definitions vary considerably. In fact, there are some implicit uses of rationality in all textbooks although these are not always acknowledged. This complexity is reflected in the history of economic thought and modern economic analysis. The future use of rationality as a teaching tool is discussed in the context of current research in economics. JEL Classification: A22