The ZINC Database contains commercially available compounds for structure based virtual screening. It currently has about 21 million compounds that can simply be purchased. It is provided in ready-to-dock, 3D formats with molecules represented in biologically relevant forms. It is available in subsets for general screening as well as target-, chemotype- and vendor-focused subsets. ZINC is free for everyone to use and download at the website zinc.docking.org. This database and service is provided by the Shoichet Laboratory in the Department of Pharmaceutical Chemistry at the University of California San Francisco (UCSF).