In common law, posse comitatus (Latin for "the power of the county") refers to the authority wielded by the county sheriff to conscript any able-bodied male over the age of fifteen to assist him in keeping the peace or to pursue and arrest a felon; compare hue and cry: A posse is the law enforcement equivalent of summoning the militia for military purposes.

The sheriff and his posse rode out to look for the bank robbers.

A posse is the body of persons that a peace officer of a U.S. county is empowered to call upon for assistance in preserving the peace, making arrests, and serving writs.

The assembled group is called a posse for short.