  We present an axiomatic framework for thermodynamics that incorporates
information as a fundamental concept. The axioms describe both ordinary
thermodynamic processes and those in which information is acquired, used and
erased, as in the operation of Maxwell's demon. This system, like previous
axiomatic systems for thermodynamics, supports the construction of conserved
quantities and an entropy function governing state changes. Here, however, the
entropy exhibits both information and thermodynamic aspects. Although our
axioms are not based upon probabilistic concepts, a natural and highly useful
concept of probability emerges from the entropy function itself. Our abstract
system has many models, including both classical and quantum examples.
