New in paperback. Hardcover was published in 2014. Phase Theory is the latest empirical and conceptual innovation in syntactic theory within the Chomskyan generative tradition. Adopting a cross-linguistic perspective, this book provides an introduction to Phase Theory, tracing the development of phases in minimalist syntax. It concludes with a discussion of some of the more contentious issues in Phase Theory, involving cross-linguistic variation with respect to phasehood and the dynamic versus static nature of phases.