This book constitutes the refereed proceedings of the 23rd International Conference on Computing and Combinatorics, COCOON 2017, held in Hiong Kong, China, in August 2017. The 56 full papers papers presented in this book were carefully reviewed and selected from 119 submissions. The papers cover various topics, including algorithms and data structures, complexity theory and computability, algorithmic game theory, computational learning theory, cryptography, computational biology, computational geometry and number theory, graph theory, and parallel and distributed computing.