To Whom It May Concern, I would like to announce the availability of my recently completed Master's thesis (written under the supervision of Steve Awodey) on the algebraic set theory website: http://www.phil.cmu.edu/projects/ast/ The title and abstract are included below in plain text. Best regards, Michael Warren -- Title: Predicative Categories of Classes. Abstract: In this thesis the tools of category theory and categorical logic are employed in order to study predicative set theories. Specifically, we introduce two constructive set theories BCST and CST and prove that they are sound and complete with respect to models in categories with certain structure. Specifically, _basic categories of classes_ and _categories of classes_ are axiomatized and shown to provide models of the aforementioned set theories. We then show that given any Heyting pretopos E there exists a subcategory Idl(E) of sheaves on E, called the _ideal completion of_ E, which is such a category of classes. Specifically, we construct fixed points for the powerobject functor P(-): Idl(E) --> Idl(E) in order to build models of the untyped set theory BCST. Furthermore, if E is a locally cartesian closed pretopos, then the construction yields models of CST inside Idl(E). Finally, it is a consequence of this work that the set theories in question are sound and complete with respect to such models in categories of ideals. This embedding results serves to establish, in effect, the conservativity of the set theory CST over a form of dependent type theory. Additional minor results which may (or may not) be of independent interest are also obtained regarding the categories in question.