  Let (M,g_0) be a compact Riemannian manifold with pointwise 1/4-pinched
sectional curvatures. We show that the Ricci flow deforms g_0 to a constant
curvature metric. The proof uses the fact, also established in this paper, that
positive isotropic curvature is preserved by the Ricci flow in all dimensions.
We also rely on earlier work of Hamilton and of Bohm and Wilking.
