  I review the observational evidence for spiral structure in the accretion
discs of cataclysmic variables (CVs). Doppler tomography is ideally suited to
resolve and map such co-rotating patterns and allows a straightforward
comparison with theory. The dwarf nova IP Pegasi presents the best studied
case, carrying two spiral arms in a wide range of emission lines throughout its
outbursts. Both arms appear at the locations where tidally driven spiral waves
are expected, with the arm closest to the gas stream weaker in the lines
compared to the arm closest to the companion. Eclipse data indicates
sub-Keplerian velocities in the outer disc. The dramatic disc structure changes
in dwarf novae on timescales of days to weeks, provide unique opportunities for
our understanding of angular momentum transport and the role of density waves
on the structure of accretion discs.
  I present an extension to the Doppler tomography technique that relaxes one
of the basic assumptions of tomography, and is able to map modulated emission
sources. This extension allows us to fit anisotropic emission from, for
example, spiral shocks, the irradiated companion star and disc-stream
interaction sites.
