This book constitutes the refereed proceedings of the 20th International Conference on Computing and Combinatorics, COCOON 2014, held in Atlanta, GA, USA, in August 2014. The 51 revised full papers presented were carefully reviewed and selected from 110 submissions. There was a co-organized workshop on computational social networks (CSoNet 2014) where 8 papers were accepted. The papers cover the following topics: sampling and randomized methods; logic, algebra and automata; database and data structures; parameterized complexity and algorithms; computational complexity; computational biology and computational geometry; approximation algorithm; graph theory and algorithms; game theory and cryptography; scheduling algorithms and circuit complexity and CSoNet.