Assistant chief constable (ACC) is the third highest rank in all British territorial police forces (except the Metropolitan Police and City of London Police, in which the equivalent rank is commander), as well as the British Transport Police, Ministry of Defence Police and Civil Nuclear Constabulary.

Each force has between one and six assistant chief constables. They are the lowest officers at chief officer level, below the chief constable and deputy chief constable, and rank immediately above chief superintendents. Assistant chief constables usually hold portfolios (e.g. for crime, operations or territorial policing). In larger forces, ACCs may be given responsibilities for policing major territories within the force area.

Senior police civilian staff (such as directors of finance and resources) hold equivalent status and are generally known as assistant chief officers.