NCIS revolves around the special agents from the Naval Criminal Investigative Service as they solve crimes involving Marine and Navy personnel. It's also the second-longest-running scripted, non-animated U.S. primetime TV series currently airing, behind only Law & Order: Special Victims Unit, and it looks like it will be continuing for another season. CBS has elected to renew the long-running series for a 19th season, ending months of speculation that the 18th season might have been its last.
There had also been rumblings that Mark Harmon, who has played Leroy Jethro Gibbs since the very beginning, would be leaving the series, but THR has reported that CBS has made a deal with the actor to return. It's said that Harmon was informed that CBS would likely cancel NCIS if he left, which is what prompted him to enter talks. Seems a little underhanded to me, but there you go. It's also not yet clear if Mark Harmon will be returning to the series full-time, as it's possible that he may only appear in a limited number of episodes. Even after all these years, NCIS remains a hugely popular series for CBS, but when you consider how the contracts for the talent and producers have grown over the past two decades, it's easy to see why the series is one of CBS' most expensive shows.
As for the rest of the NCIS franchise, it's already been announced that NCIS: New Orleans will come to an end with its seventh season, with NCIS: Los Angeles is still waiting on a renewal. There's also another spin-off, NCIS: Hawaii, in the works as well. In addition to the NCIS renewal, CBS has also renewed Magnum P.I., S.W.A.T., Blue Bloods, and Bull.