Covering linguistic research on empty categories over more than three decades, this monograph presents the result of an in-depth syntactic and focus-theoretical investigation of ellipsis in generative grammar. The phenomenon of ellipsis most generally refers to the omission of linguistic material, structure and sound. The central aim of this book is to explain on the basis of linguistic theorizing of how it is possible that we understand more than we actually hear. The answer developed throughout this book is that ellipsis is an interface phenomenon which can only be explained on the basis of the complex interaction between syntax, semantics and information structure. Scholars of grammar and cognitive scientists will profit from reading this book.