This book constitutes the proceedings of the 5th International Conference, FUN 2010, held in June 2010 in Ischia, Italy. FUN with algorithms is a three-yearly conference that aims at atractings works which, besides a deep and interesting algorithmic content, also present amusing and fun aspects. The 32 full papers and 3 invited talks are carefully selected from 54 submissions and focus on topics such as distibuted algorithms, graph computations, parallelism, zero-knowledge proof, iphone, pattern matching and strategy games.