Research on theoretical aspects of computing has a direct impact on the pr- tice of computer systems development. Over many decades, fundamental t- ories have emerged to describe functionality, temporal behavior and resource consumption. Theories of application domains are beginning to be exploited for modelling and analyzing intended computing systems before the expensive c- mitment is made to real programs and hardware. Recent years have seen major improvements in the cost-e?ectiveness of tools supporting the exploitation of theories through proof, model-checking and testing. Against this encouraging background, we are pleased to present papers that show something of the live- ness and diversity of research in theoretical aspects of computing today. ICTAC 2008, the 5th International Colloquium on Theoretical Aspects of Computing, was held on 1-3 September 2008 in Istanbul, Turkey, hosted by - banc? University. The ICTAC series was founded by the International Institute for SoftwareTechnologyof the United Nations University(UNU-IIST). It brings together practitioners and researchers from academia, industry and government to present results and to exchange ideas and experience addressing challenges in both theoretical aspects of computing and in the exploitation of theory through methodsandtoolsforsystemdevelopment. Theseriesalsopromotescooperation in research and education between participants and their institutions, from - veloping and industrial countries, in accordance with the mandate of the United Nations University. The previous ICTAC colloquia were held in Guiyang, China (2004, LNCS 3407), Hanoi, Vietnam (2005, LNCS 3722), Tunis, Tunisia (2006, LNCS 4281) and Macau SAR, China (2007, LNCS 4711).

This Festschrift, dedicated to Jan Peleska on the occasion of his 65th birthday, contains papers written by many of his closest collaborators in academic and industry research.  After studying mathematics at the University of Hamburg, Jan worked with Philips and Deutsche System-Technik on fault-tolerant systems, distributed systems, database systems, and safety-critical embedded systems. Since 1994 he has worked as a consultant to industry, specializing in development methods, verification, validation and test of safety-critical systems, and since 1995 he has been a Professor of Computer Science at the University of Bremen.  In his research he has been most interested in the combination and application of existing methods and corresponding tools to real-world problems, particularly in the field of safety-critical embedded systems and distributed systems, including avionics and railway control systems. The papers in this volume reflect those interests, and the impact he has had on colleagues and collaborators. The volume is structured into sections on testing; railway verification and safety & security; intelligent systems and cyber-physical systems; and tools and techniques for specification, verification and code generation.

This book constitutes the refereed proceedings of the 4th International Conference on Reliability, Safety, and Security of Railway Systems, RSSRail 2022, held in Paris, France, in June 2022. The 16 full papers presented in this book were carefully reviewed and selected from numerous submissions. They cover a range of topics including railways system and infrastructure advance modelling; scheduling and track planning; safety process and validation; modelling; formal verification; and security.