NCIS, Naval Criminal Investigative Service, is a CBS military television police series, revolving around a fictional team of special agents, which investigate crimes involving the U.S. Navy and Marine Corps. This group of agents is part of a major case response team based in Washington, DC and based in the Washington Navy Yard. NCIS is the primary law enforcement and counterintelligence arm of the United States Department of the Navy, which includes the United States Marine Corps. These investigators are responsible for all major criminal offenses for example, crimes punishable under the Uniform Code of Military Justice by confinement of more than one year within the Department of the Navy.

This show has been on the air since September 2003 and was a spinoff of the CBS series JAG. Now is its fourteenth season, NCIS has two very successful spinoffs, NCIS Los Angeles and NCIS New Orleans. These spinoffs periodically have crossover episodes. The original cast starred: Mark Harmon as Leroy Jethro Gibbs, Senior Special Agent assigned to Washington’s Navy Yard, Sasha Alexander as Caitlin Todd, former Secret Service Agent recruited to NCIS, Michael Weatherly as Anthony DiNozzo, Special Agent, second in command, Pauley Perrette as, Abby Sciuto, Forensic Specialist attached to NCIS, and David McCallum as Dr. Donald Mallard, Chief Medical Examiner. Supporting cast members, Joe Spano as Tobias Fornell, Senior FBI Special Agent, and Sean Murray as Timothy McGee, Probationary Agent who works at the Norfolk Naval Base became regulars during the first season. Special Agent Ziva David (Cote de Pablo), a former Mossad assassin, joined the cast after Sasha Alexander was murdered at the end of season two and was replaced by Emily Wickersham as Eleanor Bishop, Special Agent, at the end of season eleven. At the end of last season Michael Weatherly left the show and was replaced by Wilmer Valderrama, and Jennifer Esposito.

Presently, NCIS is the second longest-running scripted, non-animated U.S. primetime TV series currently airing and is the 15th longest-running scripted U.S. primetime TV series overall.