This book constitutes the refereed proceedings of the 13th International Workshop on Algorithms in Bioinformatics, WABI 2013, held in Sophia Antipolis, France, in September 2013. WABI 2013 is one of seven workshops which, along with the European Symposium on Algorithms (ESA), constitute the ALGO annual meeting and highlights research in algorithmic work for bioinformatics, computational biology and systems biology. The goal is to present recent research results, including significant work-in-progress, and to identify and explore directions of future research. The 27 full papers presented were carefully reviewed and selected from 61 submissions. The papers cover all aspects of algorithms in bioinformatics, computational biology and systems biology.