NCIS, promoted as Navy NCIS in its first season, aka Navy NCIS: Naval Criminal Investigative Service or NCIS: Naval Criminal Investigative Service, is an American police procedural television series revolving around a fictional team of special agents from the Naval Criminal Investigative Service, which conducts criminal investigations involving the U.S. Navy and Marine Corps.

The concept and characters were initially introduced in a two-part episode of the CBS series JAG (episodes 8.20 and 8.21). The show, a spin off from JAG, premiered on September 23, 2003 on CBS and, to date, has aired five full seasons. Donald Bellisario, who created JAG, as well as the well-known series and Quantum Leap, executive produces NCIS. NCIS was originally referred to as “Navy NCIS”. However "Navy" was later dropped, as it was redundant.
NCIS returned for its sixth season on September 23, 2008.