A civil, non-paramilitary police force consisting of police officers called constables. This is the usual definition in Britain, in which all county police forces once bore the title (and some still do).
A military or para-military type force consisting of soldiers trained for police duties. These were mostly established by the United States in the several countries it had protective status over (e.g. Philippine Constabulary, United States Constabulary in West Germany after World War Two, Nicaraguan National Guard, Panama National Guard). These forces also performed military functions by maintaining "mobile forces" of organised units. In Europe such forces are called Gendarmeries or (in Italy) Carabinieri.
By 1948, German police assumed the Constabulary's old police and border missions, while the remaining constabulary regiments were strengthened for possible combat by adding reconnaissance, rifle, and weapons platoons to each line troop.
The 2d Constabulary Brigade, with the 15th and 24th Constabulary Squadrons, were the last operational units and continued until their inactivation in December 1952.
Headquarters and Headquarters Troop, U.S. Constabulary was organized much as a conventional corps headquarters, but was supported by special troops with an emphasis on communications and intelligence (both criminal investigation and counterintelligence assets) activities to assist its mission as a security force.
One of the most significant developments in the history of the constabulary during the 19th century was its redesignation as the Royal Irish Constabulary, making it the first 'Royal' police force in the British Empire.
This was subsequently accepted by the government and from 1865 the policing of Belfast was left entirely to the Constabulary of Ireland (which was soon to become the Royal Irish Constabulary).
The Constabulary had settled down to low-key routine policing, with the members of the force enjoying a position of high regard in the local areas in which they served.