Skein modules are certain families of vector spaces spanned by embedded links or graphs in a 3-manifold M, modulo certain local relations. They can be thought of both as an obstruction to defining a polynomial invariant of knots in M and as an invariant of the 3-manifold M. In this talk, I will survey some history, recent results, and work in progress on skein modules, motivated by their role in the geometric Langlands program. I will discuss joint work with (some subsets of) David Ben-Zvi, David Jordan, Pavel Safronov, Monica Vazirani, and Haiping Yang.