  Understanding the superconducting properties of MgB_2 is based strongly on
knowledge of its electronic structure. In this paper we review experimental
measurements of the Fermi surface parameters of pure and Al-doped MgB_2 using
the de Haas-van Alphen (dHvA) effect. In general, the measurements are in
excellent agreement with the theoretical predictions of the electronic
structure, including the strength of the electron-phonon coupling on each Fermi
surface sheet. For the Al doped samples, we are able to measure how the band
structure changes with doping and again these are in excellent agreement with
calculations based on the virtual crystal approximation. We also review work on
the dHvA effect in the superconducting state.
