The 15th Annual International Conference on Combinatorial Optimization and Applications (COCOA 2021) will be held during December 17-19, 2021 in Tianjin, China. Original research papers in the areas of combinatorial optimization and its applications are solicited. In addition to theoretical results, we are particularly interested in submissions that report on experimental and applied research of general algorithmic interest. Special consideration will be given to research that is motivated by real-world problems. Experimental and applied papers are expected to show convincingly the usefulness and efficiency of the algorithms discussed in a practical setting.