  In this review, we summarize exact results for the three-dimensional BTZ
black hole. We use rigorous mathematical results to clarify the general
structure and properties of this black hole spacetime and its microscopic
description. In particular, we study the formation of the black hole by point
particle collisions, leading to an exact analytic determination of the Choptuik
scaling parameter. We also show that a `No Hair Theorem' follows immediately
from a mathematical theorem of hyperbolic geometry, due to Sullivan. A
microscopic understanding of the Bekenstein-Hawking entropy, and decay rate for
massless scalars, is shown to follow from standard results of conformal field
theory.
