The Mentalist follows Simon Baker as Patrick Jane, an independent consultant for the California Bureau of Investigation (CBI) based in Sacramento, California. Although not an officer of the law of any sort, he uses skills and knowledge from his former career as a successful psychic medium (this was a ruse; he does not believe anyone actually has psychic abilities) to help a team of CBI agents solve various crimes, with the hope of one day bringing his wife and daughter's murderer to justice.
It is revealed that Jane used to be a con man with a lucrative career pretending to be a psychic medium and enjoyed near-celebrity status. He appeared on television to claim that his paranormal abilities helped the police profile a serial killer named Red John. This angered Red John, who then murdered Jane's wife and daughter as revenge. Consequently, Jane abandoned his career as a psychic with the singular pursuit of bringing Red John to justice, by teaming up with the CBI to help them solve various crimes, some including those involving Red John. He openly admits that he feigned the supernatural aspects of his skills, often explaining that "there's no such things as psychics"; however, he has genuine talents in cold reading, hypnotism, powerful skills of observation and a deep insight into the human psyche and human behavior. These skills come in handy in every episode, and his unorthodox and bizarre techniques to solve crimes often clash with the agents he helps, because they often involve elaborate ruses and mind games to trick the culprit into revealing himself. Ultimately, his input to the team's work is almost always instrumental in closing the case.
The pilot episode had an audience of 15.6 million viewers in its first airing, and 7.8 million in a re-airing three days later.  It also introduced some of Jane's backstory, indicating that his wife and daughter had been murdered by a serial killer known as "Red John" five years before the series began.
On October 15, 2008, CBS ordered a full season of The Mentalist. The December 2, 2008, episode ("Flame Red") was the highest-rated television show of the week, marking the first time a program in its first season had achieved that distinction since Desperate Housewives four years earlier.
On May 20, 2009, CBS renewed The Mentalist for a second season, which premiered on September 24, 2009, in the US.  and on September 22 on CTV in Canada, as well as September 28, 2009, in Australia.
In Italy, it has been aired from April 28, 2009, on Mediaset pay-per-view Joi on the Premium Gallery and as of September 2, 2009, on Mediaset Commercial channel Italia 1. No date has been announced for other regions.
The series has moved to Thursdays at 10 p.m. ET, following CSI but now The Mentalist will move to 9/8c, before CSI. 
On November 6, 2009, TNT announced that it had obtained exclusive syndication rights for The Mentalist and would begin airing old episodes of the series starting in the Fall of 2012. 
Simon Baker as Patrick Jane – the series protagonist and the titular Mentalist. He had earned a living as a psychic, but after series antagonistRed John murders his wife and daughter in retaliation for Jane's televised mocking, Jane admits he was a fraud and now works as a police consultant for the California Bureau of Investigation. Though a bit eccentric, he is very perceptive and much of what he finds helps solve the cases they are investigating. He is brilliant and very in-tune to what is around him, but is often cocky, playful, and annoyingly right, all characteristics that earn him friendship in each of his colleagues. They are, however, often annoyed by him, to the point of taking turns of who go with him on trips. However, he has shown a much more sinister side concerning Red John, a serial killer who murdered his family. When dealing with him, Jane becomes intense, focused, and willing to sacrifice anything, including his life, to catch him.
Robin Tunney as Teresa Lisbon – though Patrick often annoys her with his unusual behavior and going behind her back, she views him as an invaluable member of the team and will back him up on some of his most unusual theories. Her mother was killed in a drunk driving accident, leaving her to take care of her brothers and her alcoholic father. She is also the only member of the team he trusts with details of his past and they work well together, despite his attitude often causing her problems with local law enforcement. Her team was responsible for the Red John case until Agent Sam Bosco became director of the new Serial Crimes Unit, which took over the responsibility for catching Red John. She and agent Bosco – Lisbon's mentor when she was a junior agent – share a dark secret which was revealed by Lisbon as leverage against Bosco in the episode 'Black Gold and Red Blood'.
Tim Kang as Kimball Cho – often portrayed as Jane's "right-hand man," he seems the closest to Jane, often requesting help regarding finding evidence, though he does get annoyed with Jane's habit of not telling him everything he knows concerning a case. Cho has a dry sense of humor and is shown to be friends with Rigsby. Probably the most down-to-earth of the group, he is often the one who sees through Jane's parlor tricks. When Jane tells Van Pelt that he was moving a straw across the table with telekinesis, Cho simply says, "He's blowing on it." He was in juvenile hall prior to serving in the military and then joining the CBI. He was secretly called "Ernie" by the Bosco team, who also refer to Rigsby as "Bert". Something he didn't mind because "Ernie's the clever, handsome one". He was in a gang called Avon Park Playboys before he was a police officer.
Owain Yeoman as Wayne Rigsby – arson specialist, he develops strong feelings for Grace Van Pelt, causing him to be overprotective of her. He didn't initially act on them, as romance between agents is against regulations, but the two gave in to their feelings and have begun seeing each other secretly. He is a good friend to Jane, though, like the others, is often annoyed by his ways. He is shown to have a good friendship with Cho. His father was a biker, which led to his own hatred of bikers. A running gag in the show is Rigsby's obsession with food. Often, during stakeouts, he is seen either eating or looking for food in the car.
Amanda Righetti as Grace Van Pelt – the newest member to the CBI, often doing research for other members. She has a deep belief in religion and psychics and will butt heads with Patrick every time he dismisses it or does something she sees as morally or religiously inappropriate. Van Pelt becomes secretly involved with Rigsby, after months of reluctance due to the regulations prohibiting romantic relationships between agents. She is very strict, organized, (Jane deduces during the first season that this is because she is hiding some deep emotional trauma) and somewhat high strung, but is overall a very valuable addition to the team.
Red John – the unseen antagonist of the series. Jane has stated that "Red John" sees himself as a "showman", as he always makes sure that his trademark, the smiley face drawn with the victim's blood, is the first thing one sees before one sees the body. The trademark face is created by using the index, middle and ring fingers of his right hand together in one motion, Red John wears rubber gloves for this act. After Jane mocked Red John on a talk show, Red John retaliated by killing Jane's wife and daughter. Though only focused on three times during the first season, he is portrayed to be very intelligent. For instance, Red John hacked into the CBI's computer system and has been using the system to monitor them for some time. So far he has been known to have three accomplices, a man that has been mentioned to have died in prison and that man's son, who held Red John in high regard. The third was revealed to be Bosco's assistant in the episode "His Red Right Hand." However, Jane states Red John doesn't have partners but tools. The episodes that Red John is involved in are gradually becoming more and more frequent as is Jane's obsession over "catching" (finding) him and "taking care of him" (killing him).
Gregory Itzin as Virgil Minelli – Minelli was the Special Agent in Charge of the CBI until the second-season episode "His Red Right Hand," wherein he retired from the CBI after the murders of Sam Bosco and his team in the same episode.
Terry Kinney as Sam Bosco – Bosco was a Senior Special Agent with the CBI. He was Lisbon's mentor when she was a junior agent. He became director of the new Serial Crimes Unit, which took over the responsibility for catching Red John. He had a severe hatred for Jane as he was not a police officer and Bosco believed he corrupted the people around him, as well as closing many cases. He also had secret feelings for Teresa (that everyone besides her seemed to notice) even though he was married. Bosco's team was murdered in the second-season episode "His Red Right Hand," shot by their secretary Rebecca (Shauna Bloom), who was a mole sent by Red John. Rebecca, in turn, was fatally poisoned by a person assumed to be Red John while being transported to prison. After she died, Jane was distraught. He visited Bosco in the hospital, where he was in critical condition following his attempted murder. He asked Jane to kill, not arrest, Red John, to which Jane responded that was always the plan. Bosco then whispered something inaudible to Jane and went into cardiac arrest. Later, the CBI team was seen mourning Bosco back at headquarters after attending his funeral.
Aunjanue Ellis as Madeleine Hightower - Hightower is the current Special Agent in Charge of the CBI, since the episode "The Red Box," wherein Jane and the rest of the team become hostile to her (Lisbon most notably). She (most of the time) is arrogant and careless about other people, due to the fact that she mysteriously found out that Rigsby and Van Pelt were having a relationship, and after informing Lisbon about the relationship, Jane points out about Hightower and says, "She's good." Most notably, she is arrogant to Jane. In the episode "Aingavite Baa", she seems to have it out against the whole team (except for Cho). She then forces Rigsby and Van Pelt to choose which one of them is going to leave the team.
The first season was released in the United states and Canada (Region 1) on September 22, 2009 and a day later in Australia (Region 4). The set, called "The Complete First Season", contains all 23 episode of the first season on 6 DVD's. The first season will be released in the UK and Ireland on March 8, 2010 and in Italy on February 23, 2010.