This book is a summary of research on second language sentence processing from the perspective of formal theories of morpho-syntax and how such theories might shed light on second language development (Chomsky, 1981, 1995; White, 2003). The book is intended to describe and summarize research that has already been published as well as some of our previously unpublished work. Within a formal framework, we address how adult users of a second language process language at the level of the sentence (usually during reading tasks), focusing on whether and how they deploy their knowledge of grammar to build a representation of the morpho-syntax of the clause being processed. Our goal is not to present a complete comparative overview of competing first and second language theories of sentence processing and acquisition. However, because the field finds itself so sharply divided, where appropriate we do refer to work in other frameworks that the interested reader should consult. We refer the reader to the excellent introduction to the edited volume by van Gompel (2013b) and papers in that volume for additional discussion on current issues in the field of sentence processing in general.