  We present a formalism for studying the thermodynamics of black holes in
dilaton gravity. The thermodynamic variables are defined on a quasilocal
surface surrounding the black hole system and are obtained from a general class
of Lagrangians involving a dilaton. The formalism thus accommodates a large
number of possible theories and black hole spacetimes. Many of the
thermodynamic quantities are identified from the contribution of the action on
the quasilocal boundary. The entropy is found using path integral techniques,
and a first law of thermodynamics is obtained. As an illustration, we calculate
the thermodynamic quantities for two black hole solutions in $(1+1)$
dimensions: one obtained from a string inspired theory and the other being a
Liouville black hole in the ``$R=\kappa T$'' theory with a Liouville field.
