NCIS is an American action police procedural television series, revolving around a fictional team of special agents from the Naval Criminal Investigative Service, which investigates crimes involving the U.S. Navy and Marine Corps. The concept and characters were initially introduced in two episodes of the CBS series JAG (season eight episodes 20 and 21: "Ice Queen" and "Meltdown"). The show, a spin-off from JAG, premiered on September 23, 2003, on CBS. To date it has aired fourteen full seasons and has gone into broadcast syndication on the USA Network. Donald P. Bellisario and Don McGill are co-creators and executive producers of the premiere member of the NCIS franchise. It is the second-longest-running scripted, non-animated U.S. primetime TV series currently airing, surpassed only by Law & Order: Special Victims Unit (1999–present), and is the 7th-longest-running scripted U.S. primetime TV series overall.
NCIS was originally referred to as Navy NCIS during season one; "Navy" was later dropped from the title as it was redundant (the "N" in "NCIS" stands for "Naval"). In season six, a two-part episode led to a spin-off series, NCIS: Los Angeles. A two-part episode during the eleventh season led to a second spin-off series, NCIS: New Orleans. While initially slow in the ratings, barely cracking the Top 30 in the first two seasons, the third season showed progress, consistently ranking in the top 20, and by its sixth season, it became a top five hit, having remained there since. In 2011, NCIS was voted America's favorite television show in an online Harris Poll. The series finished its tenth season as the most-watched television series in the U.S. during the 2012–13 TV season. On February 29, 2016, NCIS was renewed for its fourteenth and fifteenth seasons. The fifteenth season premiered on Tuesday September 26, 2017. Maria Bello joined the cast as a series regular from episode four, replacing outgoing series regular Jennifer Esposito.