BioMart is a generic data management system developed jointly by the European Bioinformatics Institute (EBI) and Cold Spring Harbor Laboratory (CSHL). It arose out of the EnsMart project designed to provide data-mining access to the Ensembl databases. The system can be used with any type of data and it comes with a range of query interfaces and administration tools, including an 'out of the box' website that can be installed, configured and customised according to requirements. The system simplifies the task of creation and maintenance of advanced query interfaces backed by a relational database and it is particularly suited for providing the 'data mining' like searches of complex descriptive (e.g. biological) data. BioMart can work with existing data repositories by converting them to a required BioMart format as well as newly created databases.