This volume constitutes the refereed proceedings of the 12th International Conference on Algorithms and Computation, ISAAC 2001, held in Christchurch, New Zealand in December 2001. The 62 revised full papers presented together with three invited papers were carefully reviewed and selected from a total of 124 submissions. The papers are organized in topical sections on combinatorial generation and optimization, parallel and distributed algorithms, graph drawing and algorithms, computational geometry, computational complexity and cryptology, automata and formal languages, computational biology...