Police ranks are a system of hierarchical relationships in police organisations. The rank system defines authority and responsibility in a police organisation, and affects the culture within the police force. Usually, uniforms denote the bearer's rank by particular insignia affixed to the uniforms.

Most of the police forces of the United Kingdom (including those of the British Overseas Territories and the Crown Dependencies) use a standardised set of ranks. However, as law enforcement in the United Kingdom is organised separately in the three jurisdictions of England and Wales, Northern Ireland, and Scotland, and as most law enforcement is carried out by police officers serving in regional police services known as territorial police forces, some variations in rank organisation, insignia and responsibilities may occur within the United Kingdom. An example of this are the slight variations in the most senior ranks of the Metropolitan Police and the City of London Police. Parallel to the regional services are UK-wide agencies, such as the British Transport Police and the national specialist units of certain territorial police forces, with a possibility of further variations.

Due to policing in many countries developing from military organisations and operations, police ranks in many countries follow a logic similar to that of military ranks. Most of the British police ranks that exist today were, however, deliberately chosen by Home Secretary Sir Robert Peel so that they did not correspond with military ranking. They were enacted under the Metropolitan Police Act 1829.