This book constitutes the refereed proceedings of the 5th International Colloquium on Theoretical Aspects of Computing, ICTAC 2008 held in Istanbul, Turkey in September 2008. The 27 revised full papers were carefully reviewed and selected from over 70 submissions. The aim of the colloquium is to bring together practitioners and researchers from academia, industry and government to present research results, and exchange experience, ideas, and solutions for their problems in theoretical aspects of computing such as automata ...