Focusing on the development of Noam Chomsky's linguistic framework, this book is the first full-length, in-depth treatment of the history of the concept of parameter, a central notion of syntactic theory. Spanning 60 years of syntactic theory, it explores all aspects of its development through the different phases of the Chomskyan school, from the 'standard theory' of the mid-1960 to the current Minimalist Program. Emphasis is put on three main topics: the foundational issues in the formulation of the Principles and Parameters model; the original formulation of the “classical” parameters of the Government-Binding Theory of the 1980s (which are then evaluated from the perspective of Chomskyan thought today), and current debates on the nature of parametric variation in light of Generative Grammar's most recent theoretical developments. Through step-by-step, detailed explanations, it provides the reader with a comprehensive account of both parametric theory and the development of Generative Grammar.