This book constitutes the thoroughly refereed post-workshop proceedings of the 25th International Workshop on Combinatorial Algorithms, IWOCA 2014, held in Duluth, MN, USA, in October 2014. The 32 revised full papers presented were carefully reviewed and selected from a total of 69 submissions. The papers focus on topics such as Algorithms and Data Structures, Combinatorial Enumeration, Combinatorial Optimization, Complexity Theory (Structural and Computational), Computational Biology, Databases (Security, Compression and Information Retrieval), Decompositions and Combinatorial Designs, Discrete and Computational Geometry, as well as Graph Drawing and Graph Theory. IWOCA is a yearly forum for researchers in designing algorithms field to advance creativeness of intersection between mathematics and computer science. This is the first time this conference is being held in U.S.