This document outlines the six main stages in the development of ideas about language that have influenced English for Specific Purposes (ESP). It discusses: 1) Classical/traditional grammar, 2) Structural linguistics, 3) Transformational Generative (TG) grammar, 4) Language variation and register analysis, 5) Functional/Notional grammar, and 6) Discourse analysis. For each stage, it provides background information on the theories and how they related to and influenced the development of ESP.