The Protein Data Bank (PDB) archive is the single worldwide repository of information about the 3D structures of large biological molecules, including proteins and nucleic acids. It is managed by the Research Collaboratory for Structural Bioinformatics (RCSB). The RCSB PDB allows users to access data through one of two methods: Search services: to return a list of IDs (i.e. PDB IDs, chain IDs, ligand IDs), Fetch services: to return data given a ID. The API uses RESTful calls and responses are formatted in XML.