  We give a unified analysis of four-dimensional elliptic models with N=2
supersymmetry and a simple gauge group, and their relation to M-theory.
Explicit calculations of the Seiberg-Witten curves and the resulting
one-instanton prepotential are presented. The remarkable regularities that
emerge are emphasized. In addition, we calculate the prepotential in the
Coulomb phase of the (asymptotically-free) Sp(2N) gauge theory with N_f
fundamental hypermultiplets of arbitrary mass.
