  This is an introduction to accretion disk theory, with emphasis on aspects
relevant for X-ray Binaries and Cataclysmic Variables. The text corrects some
mistakes in an earlier version, which appeared in 'Lives of Neutron Stars', A.
Alpar, \"U. Kizilo\u glu and J. van Paradijs (eds.), Kluwer, Dordrecht (NATO
ASI series, 1994).
