This book constitutes the refereed post-conference proceedings of the 28th International Workshopon Combinatorial Algorithms, IWOCA 2017, held in Newcastle, NSW, Australia, in July 2017.The 30 regular papers presented in this volume together with 5 invited talks were carefully reviewed and selected from 55 submissions. They were organized in topical sessions named:  approximation algorithms and hardness; computational complexity; computational geometry; graphs and combinatorics; graph colourings, labellings and power domination; heuristics; mixed integer programming; polynomial algorithms; privacy; and string algorithms.