  We review the class of cellular automata known as lattice gases, and their
applications to problems in physics and materials science. The presentation is
self-contained, and assumes very little prior knowledge of the subject.
Hydrodynamic lattice gases are emphasized, and non-lattice-gas cellular
automata -- even those with physical applications -- are not treated at all. We
begin with a review of lattice gases as the term is understood in equilibrium
statistical physics. We then discuss the various methods that have been
proposed to simulate hydrodynamics with a lattice gas, leading up to the 1986
discovery of a lattice gas for the isotropic Navier-Stokes equations. Finally,
we discuss variants of lattice-gas models that have been used for the
simulation of complex fluids.
