NCIS or N.C.I.S. may refer to:
- Naval Criminal Investigative Service, a United States law enforcement agency that investigates crimes in the U.S. Navy and Marine Corps
- NCIS (TV series), a United States television show about a group of fictional agents of the above agency
- NCIS (soundtrack), three soundtracks of music featured on the original NCIS (TV series)
- NCIS: Los Angeles, a spin-off of the show above, a show about fictional undercover NCIS agents in Los Angeles
- NCIS (TV series), a United States television show about a group of fictional agents of the above agency
- National Criminal Intelligence Service, the predecessor to the Serious Organised Crime Agency of the United Kingdom
- New Century Infusion Solutions, Inc., a health care management organization that specializes in cancer care