  We review the main observational characteristics of AM Herculis stars
(polars) at X-ray, EUV, UV, IR and optical wavelengths. Particular emphasis is
given to multi-epoch, multi-wavelength observations of the eclipsing polar HU
Aqr (RX J2107.9-0518).
  In AM Herculis stars the broad-band spectral energy distribution from X-rays
to the IR is governed by only very small structures: the hot accretion regions
on the footpoints af accreting field lines. The most extended structures in the
binary systems on the other hand, the mass-donating secondary stars and the
accretion streams, distinctly appear only as Doppler-shifted emission or
absorption lines. They can best be studied by investigating selected narrow
spectral features in the optical, ultraviolet or the near infrared.
  In this contribution both aspects will be highlighted, the structure of the
accretion regions as inferred from multi-wavelength observations with low or no
spectral resolution, as well as the structure of the secondary stars and the
accretion streams as inferred from high-resolution spectral observations and
Doppler mapping.
