Season 1
The first season of Dexter is an adaptation of Jeff Lindsay's first novel in the Dexter series, Darkly Dreaming Dexter. Subsequent seasons have featured original storylines. This season aired from October 1, 2006 to December 17, 2006, and follows Dexter's investigation of "The Ice Truck Killer". Introduced in the first episode, "Dexter", this serial killer targets prostitutes and leaves their bodies severed and bloodless. At the same time, Dexter's foster sister, Debra Morgan (Jennifer Carpenter), a vice squad officer, aspires to work in the homicide department, and Dexter's girlfriend, Rita Bennett (Julie Benz), wants their relationship to be more intimate. Christian Camargo appears as Rudy Cooper and is a recurring character until the end of the season.
Season 2
The second season of Dexter premiered on September 30, 2007, and ended on December 16, 2007. "It's Alive", the season premiere, attracted 1.09 million viewers in the United States, making Dexter the first Showtime series to attract more than a million viewers with a season premiere. The season finale, "The British Invasion", attracted 1.4 million viewers, making it the program's most-watched episode until the airing of the season three finale, "Do You Take Dexter Morgan?". Including digital video recorder (DVR) usage, season two was watched by an average of 2.4 million viewers on a weekly basis through 11 full weeks, outperforming season one by 21%. The season received universal acclaim from critics, and was praised as "one of the best shows on TV this decade" by the Chicago Sun-Times, while Variety considers Hall's portrayal of the title character as a "towering achievement, one that eclipses the show's other shortcomings and rough patches" the aggregate site Metacritic scored the season at 85 out of 100 based on 11 reviews.
Season 3
The third season of Dexter premiered on September 28, 2008, and ended on December 14, 2008. "Our Father", the season premiere, attracted 1.22 million viewers in the United States, making it Showtime's highest-rated drama season premiere since Nielsen Media Research began compiling ratings in 2004. The season's finale, "Do You Take Dexter Morgan?" attracted 1.5 million viewers. Season three was watched by an average of 1.1 million viewers a week. It received some mixed emotions from critics, which ranged from being praised as "truly and incredibly exciting television" in the San Francisco Chronicle, to "lack[ing] the crackling tension the drama had supplied in previous years" by the Chicago Tribune; the aggregate site Metacritic scored the season at 78 out of 100 based on 13 reviews.
Season 4
On October 21, 2008, Showtime commissioned a fourth and fifth season of Dexter, each consisting of 12 episodes. The show's writers convened during February and March 2009 to brainstorm ideas for the fourth season, and filming was scheduled to begin in June 2009. On May 27, 2009, Showtime announced that John Lithgow would guest star in all 12 episodes as Miami's latest and deadliest serial killer, and Keith Carradine would return as Lundy. The fourth season premiered on September 27, 2009, and focused on Dexter attempting to find his way to balance his family life, the birth of his son, and his "extra-curricular" activities. The season received positive reviews before airing, including one from Michael Ausiello of Entertainment Weekly, who saw the fourth season as being "bloody promising". The season opener was leaked to the Internet ahead of schedule in late August 2009. The fourth season premiered in the UK on the FX channel on August 20, 2010.
Season 5
The fifth season of Dexter premiered on September 26, 2010, and consisted of 12 episodes. The season focuses on how Dexter comes to terms with the aftermath of the season 4 finale, stopping a group of serial rapists and avoiding a corrupt cop who learns his deadly secret.
Season 6
The sixth season of Dexter premiered on October 2, 2011 on the television cable network Showtime, and consisted of 12 episodes. On November 18, 2011, it was announced that Dexter had been renewed for two more seasons.