The Collaborative Computational Project Number 4 (CCP4) was established in 1979 to promote collaboration between UK groups writing software for protein crystallography. CCP4 now distributes a large software suite and is active in developing new software. Equally importantly, CCP4 provides a focus for the whole protein crystallography community via meetings, workshops, email lists and various publications. In this Article, an overview is given of CCP4 activities and their administration. The emphasis is on generic features of the collaboration rather than details specific to protein crystallography. The CCP4 model has inspired similar developments in NMR, and it is hoped that the biological XAS community may pursue similar collaboration.