Pinkerton is a private security guard and detective agency established around 1850 in the United States by Scottish-born American cooper Allan Pinkerton and Chicago attorney Edward Rucker as the North-Western Police Agency, which later became Pinkerton & Co. and finally the Pinkerton National Detective Agency. At the height of its power from the 1870s to the 1890s, it was the largest private law enforcement organization in the world. It is currently a subsidiary of Swedish-based Securitas AB.

A private investigator, a private detective, or inquiry agent is a person who can be hired by individuals or groups to undertake investigatory law services. Private investigators often work for attorneys in civil and criminal cases.