This paper is a study in the grammar of coreference. A wide variety of evidence is presented which shows that the distribution of nominal expressions in English sentences if subject to previously unsuspected constraints involving coreference. Principles are suggested which explain a large number of such cases in terms of general restrictions on classes of transformations that move nominal expressions. (See AL 001 644 through AL 001 646 for other papers included in "Specification and Utilization of a Transformational Grammar.") (Author/DO)