  These lectures provide an overview of the theory of accretion disks with
application to bright sources containing black holes. I focus on the
fundamental physics of these flows, stressing modern developments and
outstanding questions wherever possible. After a review of standard
Shakura-Sunyaev based models and their problems and uncertainties, I describe
the basic principles that determine the overall spectral energy distribution
produced by the flow. I then describe the physics of angular momentum transport
in black hole accretion disks, stressing the important role of magnetic fields.
Finally, I discuss the physics of radiation magnetohydrodynamics and how it
might affect the overall flow structure in the innermost regions near the black
hole.
