This book is an extensively revised version of the core part of my 1993 MIT doctoral dissertation, which seeks to provide a Minimalist theory of Case absorption and support it through empirical investigation. The central idea pursued is that impoverishment of phrase structure is responsible for Case absorption and that the right theory of Case checking should derive this property. Although the basic line of research on Case absorption and wh-agreement remains the same, this book incorporates a lot of new results. A principied theory of Case checking and Case absorption has been worked out in Chapter 1. Treatment of participial constructions in Chapter 3 and wh agreement in Chapter 4 is far more systematic and comprehensive. Chapter 2 is also streamlined, together with refinements of the analysis of Romanian. The product, I hope, is a more convincing def ense of the strength of the Mi ni mal ist approach. I would like to thank my thesis committee members Ken Haie, Noam Chomsky, and Howard Lasnik, under whose guidance this project started.