NCIS season 21

The twenty-first season of the American police procedural television drama series NCIS was announced on February 21, 2023, by CBS, and premiered on February 12, 2024, and concluded on May 6, 2024. This is the first season not to feature David McCallum (as Dr. Donald "Ducky" Mallard), who died on September 25, 2023, though he is still posthumously credited in the first two episodes. Due to the 2023 Writers Guild of America and SAG-AFTRA strikes, the season consists of only 10 episodes, the shortest amount in the show's history, thereby beating the record previously held by the eighteenth season which was shortened due to the COVID-19 pandemic in the United States. This season also includes the 1,000th episode of the entire NCIS franchise, which aired on April 15.

On April 9, 2024, CBS renewed the show for a 22nd season.

Premise
NCIS revolves around a fictional team of special agents from the Naval Criminal Investigative Service, which conducts criminal investigations involving the United States Navy and Marine Corps. Based at the Washington Navy Yard in Washington, D.C., the NCIS team is led by Supervisory Special Agent Alden Parker, an ex-FBI Special Agent and a skilled investigator.

Main

 * Sean Murray as Timothy McGee, NCIS Senior Special Agent, second in command of MCRT
 * Wilmer Valderrama as Nick Torres, NCIS Special Agent
 * Katrina Law as Jessica Knight, NCIS Special Agent
 * Brian Dietzen as Dr. Jimmy Palmer, Chief Medical Examiner for NCIS
 * Diona Reasonover as Kasie Hines, Forensic Specialist for NCIS
 * David McCallum as Dr. Donald "Ducky" Mallard, NCIS Historian and former Chief Medical Examiner (episodes 1–2; credit only due to McCallum's death in 2023)
 * Rocky Carroll as Leon Vance, NCIS Director
 * Gary Cole as Alden Parker, Supervisory Special Agent (SSA) of the Major Case Response Team (MCRT) assigned to Washington's Navy Yard and former FBI Special Agent.

Special guest star

 * Michael Weatherly as Anthony DiNozzo, former NCIS Senior Special Agent

Notable guests

 * Joe Spano as Tobias Fornell, Private Detective and former FBI Senior Special Agent
 * Al Sapienza as Maurice Riva
 * Kim Matula as former FBI Agent Rose
 * Michael Garza as Reymundo De Leon
 * Chris Petrovski as Lev Trotski
 * David Starzyk as Allan Berger, US councilman
 * Chris McKenna as Eric Webb, former NCIS agent turned CIA agent
 * Jake Thomas as Derek Bailey, Navy Petty Officer
 * Russell Wong as Feng Zhao, NCIS Special Agent in Charge and Knight's father
 * Margo Harshman as Delilah Fielding-McGee, DoD Intelligence Analyst and McGee's wife
 * TJ Thyne as Fletcher Voss, CEO of Bandium
 * Christina Kirk as Dr. Clara Logan
 * Tim Russ as Dr. Erik Harper
 * Alastair Duncan as Ron Davenport

NCIS: Hawaiʻi

 * Vanessa Lachey as Jane Tennant, NCIS Special Agent in Charge

NCIS: Los Angeles

 * Daniela Ruah as Kensi Blye, NCIS Special Agent

Production
On February 21, 2023, NCIS was renewed for a twenty-first season, which premiered on February 12, 2024. The production of the season was delayed due to the WGA and SAG-AFTRA strikes in the United States.

David McCallum, who played Dr. Donald "Ducky" Mallard in the show's first 20 seasons, died on 25 September 2023. The second episode of the season paid tribute to him with various clips from past episodes to celebrate Ducky's life and memories with the team, as well as the appearance of former cast member Michael Weatherly, with DiNozzo showing support to Palmer moments before the funeral.

On January 5, 2024, it was announced that NCIS: Los Angeles star Daniela Ruah would be directing an episode this season, later revealed to be episode 4, titled "Left Unsaid".

On March 14, 2024, it was revealed that both Ruah and Vanessa Lachey would make an appearance as Kensi Blye and Jane Tennant, respectively, in the 1,000th overall episode of the franchise, though neither Kensi nor Jane appeared “in person” alongside the D.C. team.