This book constitutes the refereed proceedings of the 18th Annual International Conference on Computing and Combinatorics, held in Sydney, Australia, in August 2012. The 50 revised full papers presented were carefully reviewed and selected from 121 submissions. Topics covered are algorithms and data structures; algorithmic game theory and online algorithms; automata, languages, logic, and computability; combinatorics related to algorithms and complexity; complexity theory; computational learning theory and knowledge discovery; cryptography, reliability and security, and database theory; computational biology and bioinformatics; computational algebra, geometry, and number theory; graph drawing and information visualization; graph theory, communication networks, and optimization.