Abstract: A billiard in domain $Q$ of $\mathbb R^{n}$ is the dynamical system generated by the motion of a point-particle moving freely inside $Q$, and being elastically reflected off the boundary $\partial Q$. The billiard dynamics depends on the geometry of $\partial Q$. To illustrate this dependence, I will first discuss the main properties of three classes of billiards: billiards in strictly convex domain with smooth boundaries, billiard in polygons and chaotic billiards. In the second part of the talk, I will focus on chaotic billiards. The most famous chaotic billiard tables are probably the Sinai table, which is a torus with a convex scatter, and the Bunimovich stadium. I'll present a proof of the hyperbolicity of these billiards, and talk about some generalizations of the Bunimovich stadium.