The series follows a group of criminal profilers who work for the FBI as members of its Behavioral Analysis Unit (BAU) using behavioral analysis and profiling to help investigate crimes and find the suspect known as the unsub (unknown subject).
The team is supervised by Unit Chief Aaron Hotchner, and later Emily Prentiss. The team included Jason Gideon, the founder of the BAU, who was known as the best profiler in the Bureau; Derek Morgan, an ex-Chicago Police officer who is an expert on obsessional crimes; Spencer Reid, an expert on geographic profiling; Jennifer Jareau (JJ), the team's communications liaison, who later becomes a profiler; Elle Greenaway, an expert on sex crimes; David Rossi, one of the original BAU agents who is also an expert in criminal profiling; Ashley Seaver, a rookie FBI agent; Alex Blake, a linguistics specialist helping with nuances in communication; Kate Callahan, a seasoned undercover agent; Tara Lewis, a forensic psychologist; Luke Alvez, an expert fugitive tracker who becomes a profiler on the team; Stephen Walker, an expert on counterintelligence; and Matt Simmons, an expert profiler who joins the team from the FBI International Response Team.