  Spectrum of the volume integral operator of the three-dimensional
electromagnetic scattering is analyzed. The operator has both continuous
essential spectrum, which dominates at lower frequencies, and discrete
eigenvalues, which spread out at higher ones. The explicit expression of the
operator's symbol provides exact outline of the essential spectrum for any
inhomogeneous anisotropic scatterer with Holder continuous constitutive
parameters. Geometrical bounds on the location of discrete eigenvalues are
derived for various physical scenarios. Numerical experiments demonstrate good
agreement between the predicted spectrum of the operator and the eigenvalues of
its discretized version.
