**Title**: The homotopy theory of differentiable sheaves

**Abstract**: Many of the topological spaces involved in geometric topology, such as spaces of embedded manifolds, have complicated topologies that are difficult to specify and to manipulate. As already observed in the work of Galatius-Madsen-Tillmann-Weiss as well as Kupers, these spaces are often much easier to construct in the topos Diff_{≤ 0} of set-valued sheaves on manifolds, and may moreover be endowed with naturally occurring smooth structures.

Viewing Diff_{≤ 0} as a subcategory of the infinity topos Diff of homotopy-type valued sheaves ― the eponymous differentiable sheaves― we will give conceptual proofs of how Diff_{≤ 0} provides a model for the theory of homotopy types, and exhibit many good formal properties of Diff_{≤ 0}, such as the fact that all filtered colimits are homotopy colimits in Diff_{≤ 0}. By endowing Diff with certain homotopical calculi, we are moreover able to obtain a generalisation of Berwick-Evans, Boavida de Brito, and Pavlov’s result that for any (paracompact Hausdorff) manifold A, and homotopy-type valued Sheaf X the mapping sheaf Diff(A,X) computes the mapping space of the underlying homotopy types of A and X.