We love a game of billiards — or at least the mathematical version of it. It's a dynamical system that's just about basic enough to study but still poses lots of open questions. In this episode of Maths on the Move we talk to Giovanni Forni about chaos, periodicity and the many things we still hope to learn about billiards. We met Giovanni at the European Congress of Mathematics (ECM) in summer this year, which we attended with kind support of the London Mathematical Society. See here for more episodes of our Euromaths series which reports on the ECM. To find out more about mathematical billiards on Plus see   Chaos on the billiards table Playing billiards on doughnuts Playing billiards on strange tables   Here are a couple of academic papers by Forni and his collaborators:   Weakly Mixing Billiards, J. Chaika, G. Forni Weak Mixing in rational billiards, F. Arana-Herrera, J. Chaika, G. Forni.   This content was produced with kind support from the London Mathematical Society.