This paper presents an overview of how the notion of “subject” has been defined in linguistic theory. Although the term developed out of Artistotelian logic, the use has been narrowed to refer to the grammatical relation (or function). Over the past fifty years, the definition of subject and its universality has been the source of much debate. Broadly Chomskian approaches claim that grammatical relations such as subject are not primitives of the grammar and can be derived from phrase structure. As such, testing for the subject involves constituency tests. Other approaches (Relational Grammar, Lexical-Function Grammar) posit grammatical relations as primitives of the grammar and not related to constituency. And at the other extreme, certain linguists argue that subjects are not found in all languages and therefore the notion is not one of interest (Role and Reference Grammar). This paper reviews the various analyses of subjects and considers in some detail how the notion of subject has evolved within the Chomskian framework.