  Using ideas employed in higher dimensional gravity, non-expanding, weakly
isolated and isolated horizons are introduced and analyzed in 2+1 dimensions.
While the basic definitions can be taken over directly from higher dimensions,
their consequences are somewhat different because of the peculiarities
associated with 2+1 dimensions. Nonetheless, as in higher dimensions, we are
able to: i) analyze the horizon geometry in detail; ii) introduce the notions
of mass, charge and angular momentum of isolated horizons using geometric
methods; and, iii) generalize the zeroth and the first laws of black hole
mechanics. The Hamiltonian methods also provide, for the first time,
expressions of total angular momentum and mass of charged, rotating black holes
and their relation to the analogous quantities defined at the horizon. We also
construct the analog of the Newman-Penrose framework in 2+1 dimensions which
should be useful in a wide variety of problems in 2+1 dimensional gravity.
