This book contains a series of essays that explore the foundations, developments, and goals of Phase Theory. The antecedents of this framework go back to the notion of “cycle”, which plays a key role in phenomena such as compositionality, locality, and economy conditions. Much recent work within minimalism has been devoted to investigating the nature of phases and their relevance for other areas of linguistic inquiry. This book aims to address these questions and sharpen our understanding about Phase Theory and the nature of the Faculty of Language.