  This is the third article in the collection of reviews "Exact results on N=2
supersymmetric gauge theories", ed. J. Teschner. It is explained how to compute
the instanton partition functions. The results can be written as sums over
bases for the equivariant cohomology of instanton moduli spaces. The known
results relating the symmetries of these spaces to the symmetries of conformal
field theory are reviewed.
