The character "Penelope Garcia" was supposed to be in only one episode, but she tested so positively that she was added to the main cast.

Most of the playful banter between Morgan (Shemar Moore) and Garcia (Kirsten Vangsness) stems from the way the actor and actress talk to each other in real-life.

When David Rossi (Joe Mantegna) joins the team, he makes a comment that their offices are better than "that bunker", out of which the B.A.U. used to work. The comment isn't metaphorical. The actual B.A.U. (in its many earlier incarnations and titles) used to operate out of a bunker, former F.B.I. Director J. Edgar Hoover had built below F.B.I. Headquarters in Quantico, Virginia.

Matthew Gray Gubler does not wear matching socks, because he thinks it's unlucky. In a few of the episodes, you can see his mismatched socks.

J.J.'s children are played by A.J. Cook's actual children, Mekhai Andersen and Phoenix Anderson. Thomas Gibson's son Travis Gibson appeared in an episode that he directed. Joe Mantegna's daughter Gia Mantegna made a few guest appearances.

When Matthew Gray Gubler initially auditioned for the show, he was told that he was not right for the part. However, he was called back to audition again a few more times and was consistently told that he wasn't right for the part. After several more auditions, Gubler was eventually given the role.

The character of Special Agent Reid was a child prodigy, having graduated from high school at age twelve. Matthew Gray Gubler, describing what may form his character's genius, has said that Reid may have Asperger's syndrome, and perhaps even be mildly schizophrenic. Reid's mother was schizophrenic herself.

David Rossi has mentioned he knows Ringo Starr. There is even a picture of him and Starr on Rossi's desk. Joe Mantegna and Ringo Starr are friends in real-life.

Penelope Garcia was hired by the F.B.I. as a technical analyst after she was arrested for illegally hacking into their computer database. She was given the choice of working for the Bureau or being sent to federal prison.

In the show's opening credits, mug shots of real-life serial killers and mass murderers are shown. Among the killers shown are John Wayne Gacy, Charles Manson, Richard Ramirez ("The Night Stalker"), Ted Kaczynski ("The Unabomber"), Timothy McVeigh, Lee Harvey Oswald, and Susan Smith.

Dr. Spencer Reid has an I.Q. of 187, an eidetic memory, and can read up to twenty thousand words per minute.

During filming, Paget Brewster would often stash things in her boots, such as her phone, scripts, and cigarettes.

Kirsten Vangsness is the only main cast member to also be in the main cast of the short-lived spin-off, Criminal Minds: Suspect Behavior (2011).

Spencer Reid and Penelope Garcia are godparents to J.J.'s son Henry.

The original title for the show was "Quantico", and the pilot was filmed in Vancouver, Canada. In the "Quantico" script, Jason Gideon was named Jason Donovan.

Mandy Patinkin (Jason Gideon) has a son named Gideon.

Before joining the B.A.U., Derek Morgan was a highly decorated member of the Chicago Police Department's bomb squad, and is an expert at defusing explosives.

Dr. Spencer Reid holds doctorate degrees in Mathematics, Chemistry, and Engineering, as well as Bachelor's Degrees in Psychology and Sociology. He is studying for a Bachelor's degree in Philosophy as well.

Kirsten Vangsness isn't formally included in the main cast until the second season.

Reid is afraid of the dark because of the "inherent absence of light".

Rossi's full name is David Stephen Rossi. Gideon named his son Stephen after Rossi.

In a 2012 interview, in New York Magazine, Mandy Patinkin said that he greatly regrets ever having accepted his role on the show: "The biggest public mistake I ever made was that I chose to do 'Criminal Minds' in the first place. I thought it was something very different. I never thought they were going to kill and rape all these women every night, every day, week after week, year after year. It was very destructive to my soul and my personality. After that, I didn't think I would get to work in television again. I'm not making a judgment on the taste (of people who watch crime procedurals). But I'm concerned about the effect it has. Audiences all over the world use this programming as their bedtime story. This isn't what you need to be dreaming about. A show like Homeland (2011) (on which Patinkin began appearing in 2011) is the antidote. It asks why there's a need for violence in the first place."

Matthew Gray Gubler was once photographed by famed photographer Mia Grace, who had a small part in the series' pilot episode.

Reid writes a letter to his mother every day so he doesn't feel so guilty about not visiting her.

Elle Greenaway is fluent in Spanish. Emily Prentiss and Spencer Reid are both fluent in multiple languages.

One of the signature images of this show is the brief shot of a business jet flying the team to a crime scene. Often these shots are paired as book-ends at the beginning and end of an episode, with voice-over of a cast member reciting a famous quotation. The jets shown are always Gulfstream products, including models G-IV, G-V, and G-450. Occasionally the shots are reversed left-to-right (for example, episodes "A Thin Line" and "I Love You, Tommy Brown"). The tail numbers shown are often registered to Gulfstream Corporation, indicating that the shots are taken from Gulfstream publicity materials.

Agents Kate Callahan and Elle Greenaway are the only agents on the team to always be referred to by their first names. The other agents throughout the series, Jason Gideon, Aaron Hotchner, Emily Prentiss, Derek Morgan, Spencer Reid, Ashley Seaver, Jennifer Jareau, Penelope Garcia, Alex Blake, Tara Lewis, Luke Alvez, and Stephen Walker, are almost always referred to by their last names. However, Agents Hotchner and Jareau are always called by their nicknames: Hotch and J.J., respectively.

CBS aired an episode after Super Bowl XLI (2007) in the hopes of transforming the series from a relatively modest hit into a top ratings performer. The episode featured cameos by Super Bowl announcers Jim Nantz and Phil Simms.

Reid has memorized all of Rossi's books and biography.

As of season thirteen, Matthew Gray Gubler and Kirsten Vangsness are the only two cast members to have remained on the show since its inception, with other members having left the show (and return in some cases), or be fired. However, because Penelope Garcia was a recurring role during the first season, it is Matthew Gray Gubler (Dr. Spencer Reid) who holds the record as the longest-running main cast member of the series.

On the show, suspects are routinely referred to as "unsubs", or unknown subjects.

Kate Callahan (Jennifer Love Hewitt) left the show after one season. She was replaced on the team by Dr. Tara Lewis (Aisha Tyler). Hewitt and Tyler played best friends and co-workers on Ghost Whisperer (2005).

Jason Gideon and David Rossi were the two Agents who formed the basis for the B.A.U. The characters, as young men, were featured in the story "Nelson's Sparrow". But the older characters were never featured together, and the actors who played them (Mandy Patinkin and Joe Mantegna) have never acted together.

J.J. collected butterflies as a child.

It was the network's decision to cast Damon Gupton for the show. Producer Erica Messer had to create the character for him to play.

Mandy Patinkin's characters in this show and Dead Like Me (2003) have many similar interests. They are both shown to be capable and enthusiastic chefs, and have an affinity for art.

Derek Morgan is from Chicago, and has Northwestern University football memorabilia on his office shelves.

Thomas Gibson and Mandy Patinkin appeared on Chicago Hope (1994).

The only series in the "Criminal Minds" franchise without an Oscar nominee in the top-billed role. Forest Whitaker (Criminal Minds: Suspect Behavior (2011)) won Best Actor for The Last King of Scotland (2006), and Gary Sinise (Criminal Minds: Beyond Borders (2016)) earned a Best Actor in a Supporting Role nomination for Forrest Gump (1994).

Emily Prentiss' birthday is October 12, 1970.

Throughout the series, we learn that Dr Spencer Reid is from Las Vegas, NV. In reality, Matthew Gray Gubler was actually born in Las Vegas, NV.

The third Touchstone, later ABC Studios-produced show not to be aired on ABC. The other two ABC Studios-produced shows that have aired and/or still airing on CBS are: The Amazing Race (2001) and Ghost Whisperer (2005).

On this show, Keith Carradine played Frank Breitkopf, a serial killer that had been killing for thirty years. On Dexter (2006), he played Frank Lundy, who hunted a serial killer that had been killing for thirty years.

Jennifer Love Hewitt, Aisha Tyler, Jamie Kennedy, and Camryn Manheim all played roles in Criminal Minds. Hewitt as SSA Kate Callahan; Tyler as Dr. Tara Lewis; Kennedy as Floyd Feylinn Ferell; and Camryn Manheim as Carla Hines. All four of them played main roles in the television show, Ghost Whisperer.

Joel Murray, who plays the Attorney General in episode 3 of season 4, "Minimal Loss," co-starred with Thomas Gibson in Dharma and Greg as Greg's best friend and law partner.

In the beginning of season five, Dr. Spencer Reid was shot in the leg. This injury was unplanned, but had to be written in because of Matthew Gray Gubler's real-life severe knee injury, which left him unable to walk for over four months. After a third surgery, Gubler started using a cane, but was unable to walk normally for the next five months. As of December 2009, he was once again able to walk unassisted.

Lola Glaudini left the series during the second season because she was unhappy living in Los Angeles, and wanted to return to her native New York City.

In an episode when Reid (Matthew Gray Gubler) is looking into a case that could involve his father, he returns to his hotel room to find Rossi and Morgan watching a soap opera (The Young and the Restless (1973)). This is a reference to Shemar Moore (Morgan), who had a recurring role on the show.

Jason Gideon and Stephen Walker are the only main characters to have died in the series. Although, Gideon didn't die while he was on the show, he died eight years after his departure. Walker joined the team halfway through season 12. His death was the first episode of season 13.

In the time between Mandy Patinkin's departure and Joe Mantegna's arrival (a span of only three episodes) Thomas Gibson received the "Starring" credit.

Derek Morgan's son, Hank Spencer Morgan, is named for both his father and Spencer Reid, Derek's "little brother".

At the beginning of filming season twelve, Thomas Gibson (Supervisory Special Agent Aaron Hotchner) was suspended from the show after a confrontation between him and a producer. After an internal investigation, and due to the fact that this was not his first altercation with a co-worker, he was terminated.

In the time between Lola Glaudini's departure from the show, and Paget Brewster's arrival, footage is used in the opening credits that originally featured Glaudini. The footage, from season one, episode three, "Won't Get Fooled Again", is digitally altered, so that Glaudini does not appear.