Source: (2004) British Journal of Criminology. 44:15-33.Procedures for dealing with complaints against the police have been at the centre of police reform fort he last half-century. This paper departs from the traditional 'who investigates' approach and managerial orthodoxy to consider the primary functions of the complaints process. Four causes of complaints are identified- unprofessional behaviour, criminal conduct, tortious action, and unacceptable policy- and four functions are considered- managerial, liability, restorative, and accountability. It is concluded that in order to effectively and efficiently deal with the various causes of complaint, the two-tier system is required to deal with complaints that allege unprofessional behaviour and criminal conduct, and a third, separate tier, is necessary to consider unacceptable police policy. (author's abstract).