This book chapter is published open access.
This brief survey describes recent progress in our understanding of a variety of equilibrium states for finite-horizon dispersing billiard maps in two dimensions. In particular, we review formulations of topological entropy and pressure for the family of geometric potentials , where denotes the unstable Jacobian of the map and . We summarize recent results, proving the existence and uniqueness of related equilibrium states for some range of , including . In this family, corresponds to the measure of maximal entropy, while corresponds to the smooth invariant measure for the billiard map. In addition, variational principles are presented which express topological notions of pressure and entropy as the supremum of their measure-theoretic counterparts.