this book constitutes the refereed proceedings of the fourth international computer science symposium in russia, csr 2009, held in novosibirsk, russia, august 18-23, 2009. the 29 revised papers presented together with 4 invited papers were carefully reviewed and selected from 66 submissions. all major areas in computer science are addressed. the theory track deals with algorithms, protocols, and data structures; complexity and cryptography; formal languages, automata and their applications to computer science; computational models and concepts; proof theory and applications of logic to computer science. the application part comprises programming and languages; computer architecture and hardware design; symbolic computing and numerical applications; application software; artificial intelligence and robotics.