This survey of the theory of mathematical billiards reflects the present state in this
very active research area. The author attempted to make the exposition as geometrical
as possible. Smooth convex billiards, billiards in polygons and polyhedra, and chaotic
dispersing billiards are treated in separate chapters. Another chapter concerns a lesser-known
topic of dual (or outer) billiards. The survey is intended for non-experts and
provides a general mathematical background for the study of billiards.