This is the first and only book to provide an introduction to the fundamental theoretical issues of phrase structure in the Principles & Parameters approach to syntax. It provides in-depth analyses of basic phrase structure concepts and detailed examinations of different theoretical positions from within the Principles & Parameters tradition. The book approaches phrase structure through close discussion of Chomsky's The Minimalist Program (1995), Kayne's Antisymmetry of Syntax (1994) and the author's own A Theory of Phrase Markers and the Extended Base (1996), with a chapter devoted to each of these books. Throughout, the focus is almost exclusively on theoretical considerations such as primitive and derived concepts, theoretical architecture, simplicity and naturalness of extensions of basic ideas, internal coherence and consistency, and explanatory adequacy, with natural language data and analysis playing virtually no role. The structuring concepts and questions include the relation of argument structure to syntactic structure; headedness and endocentricity; the status of functional versus lexical categories; X-Bar Theory; and the respective statuses of precedence and dominance.