We prove that the homotopy theory of Picard 2-categories is equivalent to that of stable 2-types.2.1. Topological spaces and nerves of 2-categories. Notation 2.1. For spaces, we work in the category of compactly-generated weak Hausdorff spaces and denote this category Top. Notation 2.2. We let sSet denote the category of simplicial sets. Notation 2.3. We let | − | and S denote, respectively, the geometric realization and singular functors between simplicial sets and topological spaces. Notation 2.4. We let Cat denote the category of categories and functors, and let 2Cat denote the category of 2-categories and 2-functors. Note that these are both 1-categories.The category of 2-categories admits a number of morphism variants, and it will be useful for us to have separate notations for these. Notation 2.5. We let 2Cat ps denote the category of 2-categories with pseudofunctors and let 2Cat nps denote the category of 2-categories with normal pseudofunctors, that is, pseudofunctors which preserve the identities strictly. We let 2Cat nop denote the category of 2-categories and normal oplax functors. Note that these are all 1-categories.The well-known nerve construction extends to 2-categories (in fact to general bicategories) in a number of different but equivalent ways [Gur09, CCG10].Notation 2.6. We let N denote the nerve functor from categories to simplicial sets. By abuse of notation, we also let N denote the 2-dimensional nerve on 2Cat ps . This nerve has 2-simplices given by 2-cells whose target is a composite of two 1-cells, as in the