The principle that no one shall be unjustly enriched at the expense of another has been invoked to rationalise the right to restitution in a number of cases which fall outside the provinces of contract and tort. This has eventually led to the recognition of an independent legal discipline known as the law of unjust enrichment. It is among the most debated private law subjects today despite its remarkably recent origin. In Malaysia, despite the increase in judicial reference to the language of unjust enrichment to justify an award of restitutionary relief, there is generally a lack of understanding about the subject and a failure to adopt a principled approach in its treatment. Therefore, it can hardly be said that Malaysia has a well-developed law of unjust enrichment, which is unfortunate given how frequently issues concerning unjust enrichment arise. This article seeks to address the problem by offering an introduction to the subject. The ensuing discussion proceeds in five parts. Part I (History) embarks on a journey through time, tracing the evolution of unjust enrichment from its beginning to its modern form. Part II (Taxonomy) examines the place of unjust enrichment within the general framework of private law and explains its differences with the more familiar disciplines such as contract and tort. Part III (Terminology), which flows from the discussions in Parts II and I, explains why it is important to speak of unjust enrichment instead of restitution. Part IV (Lessons) explains why the discussions in Parts I to III matter today. Lastly, Part V (Future) sets out certain themes that should inform future works on this subject. The last two parts will focus on the Malaysian context.