This volume constitutes the refereed proceedings of the 23rd International Colloquium on Automata, Languages and Programming (ICALP '96), held at Paderborn, Germany, in July 1996. ICALP is an annual conference sponsored by the European Association on Theoretical Computer Science (EATCS). The proceedings contain 52 refereed papers selected from 172 submissions and 4 invited papers. The papers cover the whole range of theoretical computer science; they are organized in sections on: Process Theory; Fairness, Domination, and the u-Calculus; Logic and Algebra; Languages and Processes; Algebraic Complexity; Graph Algorithms; Automata; Complexity Theory; Combinatorics on Words; Algorithms; Lower Bounds; Data Structures...