  A theory for the effect of impurity scattering on electronic Raman scattering
in unconventional superconductors is presented. The impurity dependence of the
the spectra can be used to to distinguish between conventional (anisotropic
$s-$wave) or unconventional ($d$-wave) energy gaps, and excellent agreement
with the data on three cuprate superconductors is shown for $d_{x^{2}-y^{2}}$
pairing. The full frequency dependence of the spectra can be reproduced by
including inelastic scattering due to spin fluctuations and/or Coulomb
scattering on a partially nested Fermi surface.
