CBS has declared Monday, Sept. 25 as "NCIS Day" to celebrate the show's 20th anniversary. They will kick off the event with a mini-marathon featuring the season one premiere episode. The marathon will also include the season two finale and an episode from the current season. CBS is also offering a sale on NCIS merchandise and launching a new social media experience for fans. NCIS has been a successful series for CBS and has expanded to include four other spin-offs.