This book constitutes the proceedings of the 11th International Workshop on Algorithms and Computation, WALCOM 2017, held in Hsinchu, Taiwan, in March 2017.The 35 full papers presented together with three invited talks were carefully reviewed and selected from 83 submissions. The papers are organized in topical sections on invited talks; computational geometry; combinatorial optimization; graph drawing; graph algorithms; space-efficient algorithms; computational complexity; approximation algorithms.