A mature C programming library for manipulating protein structure. The library also provides a small number of functions for handling protein sequence as well as general purpose programming and mathematics. BiopLib transparently handles PDBML (XML) format and standard PDB files. The core of the BiopLib library is a reliable PDB parser that handles alternate occupancies and deals with compressed PDB files and PDBML files automatically. The library is designed to be as flexible as possible, allowing users to handle PDB data as a simple list of atoms, or in a structured form using chains, residues and atoms.