Lie ∞-groupoids are simplicial manifolds which satisfy conditions similar to the horn filling conditions for Kan simplicial sets. Lie ∞-groupoids are to non–negatively graded dg manifolds, or L∞-algebroids, as Lie groups are to Lie algebras. In particular, there is an integration procedure based on a smooth analog of Sullivan’s realization functor from rational homotopy theory that pro- duces a Lie ∞-groupoid from dg– manifold. There is also a differentiation functor due to Sˇevera, which uses supergeometry to construct the 1-jet of a simplicial manifold. In this talk, I will present joint work (arXiv:1609.01394) in progress with Chenchang Zhu in which we study the relationship between these integration and differentiation procedures, in analogy with Lie’s Second Theorem. A crucial first step involves constructing a user–friendly homotopy theory for Lie ∞-groupoids. This is a subtle problem, due to the fact that the category of manifolds lacks limits. I will describe how results of Behrend and Getzler can be generalized to develop a homotopy theory for Lie ∞-groups/groupoids that is compatible with the well–known homotopy theory of L∞- algebras/algebroids. If time permits, I will mention some possible applications to AKSZ σ-models via Kotov–Strobl’s theory of characteristic classes for (non–trivial) Q-bundles.