  Some recent work on the thermodynamic behavior of the matrix model of
M-theory on a pp-wave background is reviewed. We examine a weak coupling limit
where computations can be done explicitly. In the large N limit, we find a
phase transition between two distinct phases which resembles a
``confinement-deconfinement'' transition in gauge theory and which we speculate
must be related to a geometric transition in M-theory. We review arguments that
the phase transition is also related to the Hagedorn transition of little
string theory in a certain limit of the 5-brane geometry.
