Symmetric functions in geometry

There have been several recent developments in which symmetric functions encode answers to sophisticated counting problems: cohomology of spaces of solutions to various matrix problems such as moduli spaces of higgs bundles, character and quiver varieties; commutative algebra problems such as coinvariant modules; knot invariants; various combinatorial problems. Usually Macdonald polynomials come up and hint at mysterious connections between these different subjects. I'll discuss some examples and try to give an overview of this field.