This book constitutes the refereed proceedings of the 4th International Colloquium on Theoretical Aspects of Computing, ICTAC 2007 held in Macau, China in September 2007.The 29 revised full papers presented together with 3 invited talks and summaries of 2 tutorials were carefully reviewed and selected from 69 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 theory and formal languages, principles and semantics of programming languages, software architectures and their description languages, software specification, refinement, and verification, model checking and theorem proving, real-time, embedded and hybrid systems, theory of parallel, distributed, and internet-based (grid) computing, simulation and modeling, and service-oriented development.