This book constitutes the refereed proceedings of the 5th International Conference on Algebraic Informatics, CAI 2013, held in Porquerolles, France in September 2013. The 19 revised full papers presented together with 5 invited articles were carefully reviewed and selected from numerous submissions. The papers cover topics such as data models and coding theory; fundamental aspects of cryptography and security; algebraic and stochastic models of computing; logic and program modelling.