This book constitutes the refereed proceedings of the 25th International Colloquium on Automata, Languages and Programming, ICALP'98, held in Aalborg, Denmark, in July 1998. The 70 revised full papers presented together with eight invited contributions were carefully selected from a total of 182 submissions. The book is divided in topical sections on complexitiy, verification, data structures, concurrency, computational geometry, automata and temporal logic, algorithms, infinite state systems, semantics, approximation, thorem proving, formal languages, pi-calculus, automata and BSP, rewriting, networking and routing, zero-knowledge, quantum computing, etc..