NCIS: Los Angeles is an American action crime drama television series combining elements of the military drama and police procedural genres, which premiered on CBS on September 22, 2009. The series follows the exploits of the Los Angeles–based Office of Special Projects (OSP), an elite division of the Naval Criminal Investigative Service that specializes in undercover assignments. NCIS: Los Angeles is the first spin-off of the successful series NCIS and the second series in the NCIS franchise. The series concluded on May 21, 2023, making it the second series in the NCIS franchise to end (first being NCIS: New Orleans).

The series starred Chris O'Donnell, Daniela Ruah, and LL Cool J alongside an ensemble cast. The first season featured Peter Cambor, Adam Jamal Craig, Linda Hunt and Barrett Foa. Cambor was demoted to recurring status, and Craig's character was killed off at the end of season 1, while Foa was written out at the end of season 12 and Hunt was demoted to "special guest star" status at the beginning of season 13. Other stars included Eric Christian Olsen, Renée Felice Smith, Miguel Ferrer, Nia Long, Medalion Rahimi, Caleb Castille, and Gerald McRaney. Cast members from the original NCIS made appearances on the series with Rocky Carroll recurring in the first three seasons, and making an appearance in season six. Cast members from non NCIS shows had also made appearances, specifically in a crossover event with Hawaii Five-0.

NCIS: Los Angeles received generally mixed reviews from critics, but became a solid ratings hit for CBS at the time of its premiere. The series received six Teen Choice Awards for Choice Action Show, Choice TV Actress Action for Hunt, and Choice TV Actor Action for LL Cool J.