This book constitutes the refereed proceedings of the 36th International Workshop on Combinatorial Algorithms, IWOCA 2025, held in Bozeman, MT, USA, during July 21-24, 2025. The 32 full papers and two abstracts of invited talks included in this book were carefully reviewed and selected from 71 submissions. The IWOCA conference series has provided an annual forum for researchers who design algorithms to address the myriad combinatorial problems underlying computer applications in science, engineering, and business.