The doctrine of legitimate expectation was first developed in English law as a ground of judicial review in administrative law to protect a procedural or substantive interest when a public authority rescinds from a representation made to a person. It is based on the principles of natural justice and fairness, and seeks to prevent authorities from abusing power.

The courts of the United Kingdom have recognized both procedural and substantive legitimate expectations. A procedural legitimate expectation rests on the presumption that a public authority will follow a certain procedure in advance of a decision being taken, while a substantive legitimate expectation arises where an authority makes a lawful representation that an individual will receive or continue to receive some kind of substantive benefit. In determining a claim for an alleged breach of a legitimate expectation, a court will deliberate over three key considerations:

Procedural legitimate expectations have been recognized in a number of common law jurisdictions. In contrast, notwithstanding their acceptance and protection in the UK, substantive legitimate expectations have not been universally recognized. For instance, they have been given effect in Singapore but not in Australia.

Since its inception, the doctrine of legitimate expectation has been viewed as an offshoot of natural justice. The duty to act fairly is a core tenet of administrative law and a predominant feature in the application of the rules of natural justice. With each individual's entitlement to natural justice and fairness, legitimate expectation reinforces the duty of public bodies to act fairly. It is this protection of fairness that made way for the courts' acknowledgement of legitimate expectations. In their elaboration of the doctrine, courts of the United Kingdom adopted other key aspects of judicial review such as Wednesbury unreasonableness, fairness, and abuse of power to justify the existence and the protection of legitimate expectations.

The term legitimate expectation was first used in the case of Schmidt v Secretary of State for Home Affairs (1968), but was not applied on the facts. Subsequently, in O'Reilly v Mackman (1983) the doctrine of legitimate expectation was recognized as part of judicial review in public law, allowing individuals to challenge the legality of decisions on the grounds that the decision-maker "had acted outwith the powers conferred upon it". Although initially unclear, the nature and boundaries of the doctrine of legitimate expectation have been elucidated by seminal cases such as Council of Civil Service Unions v Minister for the Civil Service (the GCHQ case, 1983). and R v North and East Devon Health Authority, ex parte Coughlan (1999). Notwithstanding efforts of the courts, some ambiguity as to when legitimate expectations arise persisted. In response, Lord Justice of Appeal John Laws proposed the aspiration of "good administration" as a justification for the protection of legitimate expectations.

A procedural legitimate expectation is created when a representation is made by a public authority that it will follow a certain procedure before making a decision on the substantive merits of a particular case. Examples of procedural legitimate expectations include an expectation to be consulted and to a fair hearing. A substantive legitimate expectation is formed where a representation is made by an authority as to the final decision and outcome that the authority will make in a particular case.

Upon reviewing a claim for the protection of a legitimate expectation against a public authority's decision, courts will deliberate over three key considerations:

When determining if a legitimate expectation is present, the required conditions are as follows: