We will discuss N=2 supersymmetry on compact four manifolds of toric type and how to compute the partition function of N=2 gauge theories in these cases. A general formula is presented which confirms some earlier expectations by Nekrasov and we specify in the trial cases of P^2 and P^1xP^1. These are compared respectively with Donaldson topological invariants on P^2 and with a chiral version of Liouville gravity.