FUN with Algorithms is a three-yearlyconference that aims at attracting works which, besides a deep and interesting algorithmic content, also present amusing and fun aspects, are written with a keen wit, and are presented in a lively way. FUN isactuallyone ofthe mainmovingwheelsbehind mostofthe bestscienti?c results, and in a sense this conference answers to the unconfessed need of having a place where we can present the most lighthearted part of our work without sacri?cing precision and rigor. The 5th International Conference on Fun with Algorithms (FUN 2010) was held at Hotel Continental Terme in Ischia (Italy), June 2-4, 2010. The island of Ischia, a worldwide famous spa, sea, and tourist resort, is the ideal venue to host an event dedicated to pleasure as well as to science. The call for papers attracted54 submissions from all overthe world.Subm- ted paperswerecharacterizedbyanextremely high quality andfeaturing a large variety of topics. After a careful and thorough reviewing process, the Program Committee selected 32 papers. The program also included three invited talks by Roberto Grossi, Prabhakar Raghavan, and Paul Spirakis. Extended versions of selected papers presented at the meeting will be published in a special issue of Theory of Computing Systems.