MB is a community curated database of all the biological databases available on the Internet. The aim of the project is to make it easy for researchers to quickly find relevant information about useful databases. Entries can be searched, queried or browsed by category, and users can contribute, update and maintain the data in many different ways. Each database in MB is described in a semi structured way using forms and templates. Entries carry data for various fields and allow a free text description of the resource. In detail, data for each database include a brief description, a URL, a contact email, links to associated literature and various categorization tags. In addition, entries can carry various user comments and annotations.