Abstract Motivation: Organic enzyme cofactors are involved in many enzyme reactions. Therefore, the analysis of cofactors is crucial to gain a better understanding of enzyme catalysis. To aid this, we have created the CoFactor database. Results: CoFactor provides a web interface to access hand-curated data extracted from the literature on organic enzyme cofactors in biocatalysis, as well as automatically collected information. CoFactor includes information on the conformational and solvent accessibility variation of the enzyme-bound cofactors, as well as mechanistic and structural information about the hosting enzymes. Availability: The database is publicly available and can be accessed at http://www.ebi.ac.uk/thornton-srv/databases/CoFactor Contact: julia.fischer@ebi.ac.uk Supplementary information: Supplementary data are available at Bioinformatics online.