  We study finite size effects in superconducting metallic grains and determine
the BCS order parameter and the low energy excitation spectrum in terms of
size, and shape of the grain. Our approach combines the BCS self-consistency
condition, a semiclassical expansion for the spectral density and interaction
matrix elements, and corrections to the BCS mean-field. In chaotic grains
mesoscopic fluctuations of the matrix elements lead to a smooth dependence of
the order parameter on the excitation energy. In the integrable case we observe
shell effects when e.g. a small change in the electron number leads to large
changes in the energy gap.
