The Collaborative Computational Project Number 4 (CCP4) program suite is a collection of disparate programs, which communicate via standard data files, rather than all operations being integrated into one huge program, covering most of the computations required for macromolecular crystallography. They have been collected and developed under the auspices of the Collaborative Computing Project Number 4, in Protein Crystallography, supported by the UK Science and Engineering Research Council (SERC) since 1979 and currently the Biotechnology and Biological Sciences Research Council (BBSCR), and coordinated at Daresbury Laboratory. The Project aimed to support collaboration between those working on such software in the UK, and to assemble a comprehensive collection of it to satisfy the computational requirements of the relevant UK groups. The results of this effort are also made available for distribution to academic and commercial users outside the UK. The distribution, described herein, is often loosely referred to as `CCP4', but is properly `The CCP4 Suite'.