This book constitutes the proceedings of the 25th International Conference on Computing and Combinatorics, COCOON 2019, held in Xi'an, China, in July 2019. The 55 papers presented in this volume were carefully reviewed and selected from 124 submissions. The papers cover various topics, including algorithm design, approximation algorithm, graph theory, complexity theory, problem solving, optimization, computational biology, computational learning, communication network, logic, and game theory.