  I modify the quasilocal energy formalism of Brown and York into a purely
Hamiltonian form. As part of the reformulation, I remove their restriction that
the time evolution of the boundary of the spacetime be orthogonal to the leaves
of the time foliation. Thus the new formulation allows an arbitrary evolution
of the boundary which physically corresponds to allowing general motions of the
set of observers making up that boundary. I calculate the rate of change of the
quasilocal energy in such situations, show how it transforms with respect to
boosts of the boundaries, and use the Lanczos-Israel thin shell formalism to
reformulate it from an operational point of view. These steps are performed
both for pure gravity and gravity with attendant matter fields. I then apply
the formalism to characterize naked black holes and study their properties,
investigate gravitational tidal heating, and combine it with the path integral
formulation of quantum gravity to analyze the creation of pairs of charged and
rotating black holes. I show that one must use complex instantons to study this
process though the probabilities of creation remain real and consistent with
the view that the entropy of a black hole is the logarithm of the number of its
quantum states.
