A detective is an investigator, either a member of a police agency or a private person. Private detectives usually operate commercially and are licensed. They may be known as private investigators (P.I.s or "private eyes"). Informally, and primarily in fiction, a detective is any unlicensed person who solves crimes, including historical crimes, or looks into records.

Detective as a designator of rank or status

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In some police departments, primarily in North America, Detective can be the lowest rank among investigators (above the lowest rank of officers and below Sergeant). Some departments have distinct levels of detectives, depending on their experiences and skills. New York City Police Department and Los Angeles Police Department, for example, both have three grades. Most larger police departments have rank structures for their investigators that parallel the "street" police, such as Detective Sergeant and Detective Lieutenant.

In the British police, "Detective" is used as a prefix before all ranks in the Criminal Investigation Department and Special Branch from Constable to Chief Superintendent. Detective Constables do not outrank uniformed Constables, however. In the 19th and early 20th centuries, Detective Constables were usually referred to simply as "Detective", but this is no longer the case. Many Commonwealth countries also use the prefix.

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