This volume of new work by prominent phonologists goes to the heart of current debates in phonological and linguistic theory: should the explanation of phonological variety be constraint or rule-based and, in the light of the resolution of this question, how in the mind does phonology interface with other components of the grammar. The book includes contributions from leading proponents of both sides of the argument and an extensive introduction setting out the history, nature, and more general linguistic implications of current phonological theory.