According to Sir Ivor Jennings in his book The Law and the Constitution (1959):

“Administrative Law is the law relating to the administration. It determines the organisation, powers and duties of administrative authorities.”

Jennings’ definition emphasises three aspects: (i) the organisation of administrative bodies, (ii) their powers, and (iii) their duties. The definition is often criticised as being too wide (it includes even constitutional law of administration) and silent on remedies available to citizens against administrative action; nevertheless, it is the classical starting point for the subject.