This collection of previously unpublished or hard-to-find essays traces the evolution from the mid-1980s to the present day of constraint-based grammar formalisms in general and head-driven phrase structure grammar (HPSG) in particular. HPSG is a framework for linguistic theory which is one of the principal competitors to Chomsky's transformational grammar and which is widely regarded as the most influential linguistic framework worldwide in the field of computational linguistics. Topics covered include the architecture of grammatical theory; formal foundations of linguistic theory, encompassing the model-theoretic interpretation of grammars as sets of abstract feature structures; computational complexity; lexical rules, and binding theory. The essays have all been corrected and supplied with new notes. In addition, Pollard has written a new introduction that places the essays into a historical context.