Phase Theory is the latest model of modern syntactic theorizing in the generative tradition, the larger research enterprise known as the ‘Minimalist Program.’ This volume collects current research of scholars who investigate the role of formal features in the grammar, address licensing of grammatical properties in the theoretical model, and critically inspect particular aspects of the expression of arguments within Phase Theory. The chapters provide a wealth of empirical data from typologically different languages and novel syntactic analyses drawing from all aspects of the grammar (syntax, semantics, morphology, and phonology).