Under what conditions are expressions of a language the same; when are they different? Indices and Identity focuses on this question in the context of the theory of anaphora and on the role of indices in characterizing syntactic and semantic identity of expressions. Fiengo and May develop two main themes within the theory of anaphora. The first pertains to the meaning of coindexing and non-coindexing--the correspondence between indexical relations among expressions and the valuation relation that holds among them--while the second is the development of Dependency Theory, the theory of the relations of occurrences of indices. The novelty of Fiengo and May's approach lies with their characterization of indexical dependencies and the conditions under which structures manifest the same or different dependency. In particular, Indices and Identity emphasizes issues raised by strict and sloppy identity in ellipsis, exploring what Fiengo and May call the eliminative puzzles of ellipsis. The significance of these puzzles is that they show the shortcomings of current theories of anaphora in ellipsis, while illustrating an application of Dependency Theory to complex cases of strict and sloppy identity. Elliptical contexts in turn lead to consideration of the embedding of the formal syntactic notions of identity arising from indices and dependencies within more general notions of structural identity. This relates to a consideration of the foundations of reconstruction, which, the authors argue, is syntactic identity up to indexical identity and vehicle change--variation in the syntactic form of expression of arguments.The book concludes with a discussion of the relation of reconstruction, logical representation in grammar, and the application of grammatical constraints. The discussion focuses on antecedent contained deletion, and stands independently as a comprehensive study of this construction. Linguistic Inquiry Monograph No. 24