Dexter is an American crime drama television series that aired on Showtime from October 1, 2006, to September 22, 2013. Set in Miami, the series centers on Dexter Morgan (Michael C. Hall), a forensic technician specializing in blood spatter analysis for the fictional Miami Metro Police Department, who leads a secret parallel life as a vigilante serial killer, hunting down murderers inadequately punished by the justice system due to corruption or legal technicalities. The show's first season was derived from the novel Darkly Dreaming Dexter (2004), the first in a series of novels by Jeff Lindsay. It was adapted for television by James Manos Jr., who wrote the first episode.

The series enjoyed mostly positive reviews throughout its run. The first four seasons were widely praised, but reception dropped considerably as the series progressed, with the final season and especially the series finale being highly criticized and often cited as amongst the worst of all time. The show has received myriad awards, including two Golden Globes won by Hall and John Lithgow for their roles as Dexter Morgan and Arthur Mitchell, respectively.

The fourth season aired its season finale on December 13, 2009, to a record-breaking audience of 2.6 million viewers, making it the most-watched original series episode ever on Showtime at that time. The eighth season served as the final season of Dexter ; the season premiere was the most watched Dexter episode, with more than 3 million viewers total, while the series finale drew 2.8 million viewers, the largest audience in Showtime's history.

Dexter has continued through an expanded franchise with further series. The sequel series Dexter: New Blood aired from November 2021 to January 2022, with Hall reprising the title role and Clyde Phillips as showrunner. The prequel series Dexter: Original Sin premiered in December 2024, starring Patrick Gibson as Dexter. Further series are in development, including Dexter: Resurrection, and Trinity Killer, a spin-off prequel series.