  The rates at which classical and quantum information can be simultaneously
transmitted from two spatially separated senders to a single receiver over an
arbitrary quantum channel are characterized. Two main results are proved in
detail. The first describes the region of rates at which one sender can send
classical information while the other sends quantum information. The second
describes those rates at which both senders can send quantum information. For
each of these situations, an example of a channel is given for which the
associated region admits a single-letter description. This is the author's
Ph.D. dissertation, submitted to the Department of Electrical Engineering at
Stanford University in March, 2005. It represents an expanded version of the
paper quant-ph/0501045, containing a number of tutorial chapters which may be
of independent interest for those learning about quantum Shannon theory.
