It gives us great pleasure to present the proceedings of the 4th Workshop on Algorithms in Bioinformatics (WABI 2004) which took place in Bergen, Norway, September 17 21, 2004. The WABI 2004 workshop was part of a ?- conference meeting, which in addition to WABI, included ESA, WAOA, IWPEC, and ATMOS, hosted by the University of Bergen, Norway. See http: //www.ii.uib.no/algo2004/ for more details. TheWorkshoponAlgorithmsinBioinformaticscoversresearchonallaspects of algorithmic work in bioinformatics. The emphasis is on discrete algorithms that address important problems in molecular biology....