The two-volume set LNCS 5125 and LNCS 5126 constitutes the refereed proceedings of the 35th International Colloquium on Automata, Languages and Programming, ICALP 2008, held in Reykjavik, Iceland, in July 2008. The 126 revised full papers presented together with 4 invited lectures were carefully reviewed and selected from a total of 407 submissions. The papers are grouped in three major tracks on algorithms, automata, complexity and games, on logic, semantics, and theory of programming, and on security and cryptography foundations. LNCS 5125 contains 70 contributions of track A selected from 269 submissions as well as 2 invited lectures. The papers are organized in topical sections on complexity: boolean functions and circuits, data structures, random walks and random structures, design and analysis of algorithms, scheduling, codes and coding, coloring, randomness in computation, online and dynamic algorithms, approximation algorithms, property testing, parameterized algorithms and complexity, graph algorithms, computational complexity, games and automata, group testing, streaming, and quantum, algorithmic game theory, and quantum computing.