  These notes introduce and review some of the physical principles underlying
the theory of astrophysical accretion, emphasizing the central roles of angular
momentum transport, angular momentum loss, and radiative cooling in determining
the structure and evolution of accretion flows. Additional topics covered
include the effective viscous theory of thin disks, classical instabilities of
disk structure, the evolution of warped or eccentric disks, and the basic
properties of waves within disks.
