Gauge theory has given us three types of invariants of smooth structures of closed four-manifolds: the Donaldson invariants, the Seiberg-Witten invariants, and the less well-known spin invariants of Pidstrigach and Tyurin. The SO(3)-monopole program produces a qualitative relation between the Donaldson and Seiberg-Witten invariants as well as one between the spin and Seiberg-Witten invariants. In this talk, I will review the definition of the spin invariants and describe a program for directly comparing the spin and Donaldson invariants for smooth four-manifolds.