The Protein Data Bank (PDB) is the single worldwide database that stores the 3D structural data of large biological molecules such as proteins and nucleic acids. It contains data submitted by researchers from around the world. The PDB is operated by three member organizations and uses standardized file formats like PDB, mmCIF, and PDBML to store and represent structural data. Secondary databases categorize the PDB data in different ways, such as by structure, function, or evolutionary relationships. Visualization programs can be used to view PDB file contents. PDBWiki allows collaborative discussion and annotation of PDB structures, complementing the PDB's role as a primary data archive.