The concept of legitimate expectation, which is the subject of this chapter, is closely related to the common law principles of fairness. As an important ground of judicial review it has evolved from the mere expectation of procedural safeguards to include, in certain circumstances, a substantive dimension, as illustrated in the famous case of R v North and East Devon Heath Authority, ex p Coughlan. This pivotal decision is analysed at some length. From a wider European perspective the concept of legitimate expectation is founded on the doctrine of legal certainty and, in essence, it means that decision-makers in the public domain must operate according to established procedures, and may be bound by promises or policies, for instance, if resiling from such a promise or policy would constitute an abuse of power. The chapter goes on to discuss the development of the most important case law in the field.