  A set of boundary conditions defining a non-rotating isolated horizon are
given in Einstein-Maxwell theory. A space-time representing a black hole which
itself is in equilibrium but whose exterior contains radiation admits such a
horizon . Physically motivated, (quasi-)local definitions of the mass and
surface gravity of an isolated horizon are introduced. Although these
definitions do not refer to infinity, the quantities assume their standard
values in Reissner-Nordstrom solutions. Finally, using these definitions, the
zeroth and first laws of black hole mechanics are established for isolated
horizons.
