Here are the refereed proceedings of the 6th International Workshop on Algorithms in Bioinformatics, WABI 2006, held in the course of the ALGO 2006 conference meetings. The book presents 36 revised full papers addressing all current issues of algorithms in bioinformatics, from mathematical tools to experimental studies of approximation algorithms and reports on significant computational analyses. For the first time, coverage extends to machine-learning approaches along with combinatorial optimization.