  Black holes are thermodynamic objects, but despite recent progress, the
ultimate statistical mechanical origin of black hole temperature and entropy
remains mysterious. Here I summarize an approach in which the entropy is viewed
as arising from ``would-be pure gauge'' degrees of freedom that become
dynamical at the horizon. For the (2+1)-dimensional black hole, these degrees
of freedom can be counted, and yield the correct Bekenstein-Hawking entropy;
the corresponding problem in 3+1 dimensions remains open.
