A New Orleans, La private investigator, or PI, is a person who undertakes investigations, usually for a private citizen or some other entity not involved with a government or police organization. They often work for attorneys in civil cases or on behalf of a defense attorney. Many work for insurance companies to resolve insurance fraud claims or worker compensation claims. Before the advent of no-fault divorce, many private investigators were hired to search out evidence of adultery, infidelity, cheating spouse, cheating wife, girlfriend, cheating husband, boyfriend or other illegal conduct within marriage to establish grounds for a divorce. Despite the lack of legal necessity for such evidence any more, according to press reports collecting evidence of adultery or other "bad behavior" by spouses and partners is still one of the most profitable activities investigators undertake.

Many jurisdictions require PIs, or private eyes, to be licensed, and they may or may not carry firearms depending on local laws. Some are ex-police officers. They are expected to keep detailed notes and to be prepared to testify in court regarding any of their observations on behalf of their clients. Taking great care to remain within the law (e.g., being forbidden to trespass on private property or break into homes) is also required, on pain of losing their licenses as well as facing criminal charges. Irregular hours may also be required when performing surveillance work (e.g., outside someone's house during the early hours of the morning).

PIs in fiction

Perhaps the most famous fictional PI is the Sherlock Holmes character created by Arthur Conan Doyle, who would refer to himself in the jargon of his age as a "private inquiries agent." (See Crime fiction for details.)

Since about the 1940s, PIs have also been frequently found in fiction as a stock character; they are a hero archetype who stumbles into detective stories to solve a mystery case, whether it be a whodunit murder or other crime activity. The PI is usually cool, relaxed and intelligent. A stereotypical look would have him drink whiskey, smoke, dress in a raincoat and fedora and be a good marksman. (The pop/rock/soul duo Hall & Oates replicated the raincoat and fedora look in the print promo and MTV clips for the lead track of their Private Eyes album.)

PIs are also popular in television fiction, including such hit series as Magnum P.I., Veronica Mars, Moonlighting, Remington Steele, The Rockford Files, and Spenser: For Hire; both TV and movie PI fiction often utilize the device of the main character first-person voiceover to make up for the fact that visual fiction is rarely ever shot in the true first-person, as well as to provide exposition about the detective's thoughts. Meanwhile filmmakers like Joel and Ethan Coen (The Big Lebowski), David O. Russell (I ♥ Huckabees), and writers like Jennifer Colt (The Butcher of Beverly Hills), and Laura Anne Gilman (Staying Dead) have moved the traditional PI protagonist towards new genres.