This book constitutes the thoroughly refereed post-workshop proceedings for the 26 International Workshop on combinatorial Algorithms, IWOCA 2015, held in Verona, Italy, in October 2015.The 29 revised full papers presented were carefully reviewed and selected from a total of 90 submissions. The topics of the papers include algorithms and data structures (including sequential, parallel, distributed, approximation, probabilistic, randomised, and on-line algorithms), algorithms on strings and graphs; applications (bioinformatics, music analysis, networking, and others); combinatorics on words; combinatorial enumeration; combinatorial optimization; complexity theory; computational biology; compression and information retrieval; cryptography and information security; decompositions and combinatorial designs; discrete and computational geometry; graph drawing and labeling; graph theory.