Just as pronouns like "she" and "he" make anaphoric reference to individuals, English words like "that" and so can be used to refer anaphorically to a proposition introduced in a discourse: "That's true; She told me so". Much has been written about individual anaphora, but less attention has been paid to propositional anaphora. This dissertation is a comprehensive examination of propositional anaphora, which I argue behaves like anaphora in other domains, is conditioned by semantic factors, and is not conditioned by purely syntactic factors nor by the at-issue status of a proposition. I begin by introducing the concepts of anaphora and propositions, and then I discuss the various words of English which can have this function: "this", "that", "it", "which", "so", "as", and the null complement anaphor. I then compare anaphora to propositions with anaphora in other domains, including individual, temporal, and modal anaphora. I show that the same features which are characteristic of these other domains are exhibited by propositional anaphora as well. I then present data on a wide variety of syntactic constructions--including subclausal, monoclausal, multiclausal, and multisentential constructions--noting which license anaphoric reference to propositions. On the basis of this expanded empirical domain, I argue that anaphoric reference to a proposition is licensed not by any syntactic category or movement but rather by the operators which take propositions as arguments. With this generalization in hand, I turn to how such facts can be formally modeled: I review existing systems which track anaphora and/or which make use of propositional variables, and then introduce a new formalism which incorporates insights from these existing systems. Finally, I turn to the interaction between a proposition's availability for anaphoric reference and its discourse status (in particular, its at-issue status). Contrary to the prevailing assumption in the literature, I argue that there is no tight linking between these two properties, and that one of the tests frequently used to diagnose at-issueness in fact diagnoses only anaphoric availability. I argue that propositional anaphora and at-issueness are distinct, showing that at-issueness is neither necessary nor sufficient to determine a proposition's anaphoric potential. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]