The Introduction outlines the book’s six chapters. Chapter 1 presents the theoretical foundations of Generative Grammar and discusses the ‘prehistory’ of the concept of parameter in the late seventies and early eighties up to the formulation of the Principles and Parameters model of the Government and Binding (GB) framework. Chapter 2 examines the individual formulation of the main parameters that were proposed during that period, summarizing many of the central empirical concerns of research in the 1980s. Chapter 3 traces the development of the concept of parameter in early Minimalism, focusing on the debate over macro- vs. microparameters, the main criticisms raised against the parametric approach, and the latter’s subsequent reformulation within recent hierarchical models. Chapter 4 returns to the parameters of the GB Theory and evaluates their status in current generative theory. Chapter 5 is devoted specifically to the head-complement parameter, whose history arguably embodies the development of the parametric approach to linguistic variation. Chapter 6 draws the conclusions of the historical review conducted in the previous chapters and critically reconsiders the notion of parameter.