The Big Bang Theory is an American television sitcom created by Chuck Lorre and Bill Prady for CBS. It aired from September 24, 2007, to May 16, 2019, running for 12 seasons and 279 episodes.
The show originally centered on five characters living in Pasadena, California: Leonard Hofstadter (Johnny Galecki) and Sheldon Cooper (Jim Parsons), both physicists at the California Institute of Technology, who share an apartment; Penny (Kaley Cuoco), a waitress and aspiring actress who lives across the hall; and Leonard and Sheldon's similarly geeky and socially awkward friends and coworkers, aerospace engineer Howard Wolowitz (Simon Helberg) and astrophysicist Raj Koothrappali (Kunal Nayyar). Over time, supporting characters were promoted to starring roles, including neuroscientist Amy Farrah Fowler (Mayim Bialik), microbiologist Bernadette Rostenkowski (Melissa Rauch), and comic book store owner Stuart Bloom (Kevin Sussman).
The series was filmed in front of a live audience and produced by Chuck Lorre Productions, with Warner Bros. Television handling distribution. While the first season received mixed reviews, critical reception improved in subsequent seasons. Seven seasons ranked within the top ten of the final-season ratings, and the series reached the No. 1 spot in its eleventh season. It was nominated for the Emmy Award for Outstanding Comedy Series from 2011 to 2014 and won the Emmy Award for Outstanding Lead Actor in a Comedy Series four times for Parsons, totaling seven Emmy Awards from 46 nominations. Parsons also won the Golden Globe for Best Actor in a Television Comedy Series in 2011.
The success of The Big Bang Theory launched a multimedia franchise. A prequel series focusing on Parsons' character Sheldon Cooper, Young Sheldon, aired from 2017 to 2024, with Parsons narrating as the adult Sheldon. The third series in the franchise, a sequel to Young Sheldon titled Georgie & Mandy's First Marriage, premiered in October 2024 and follows Sheldon's older brother, Georgie, and his wife, Mandy. A fourth series, following Stuart Bloom, his girlfriend Denise, geologist Bert Kibbler, and physicist Barry Kripke, titled Stuart Fails to Save the Universe, premiered in July 2026 on streaming platform HBO Max.
Plot
Seasons 1–4 The series centers on the evolving relationships between socially awkward physicists Leonard Hofstadter and Sheldon Cooper, their neighbor Penny, and their friends Howard Wolowitz and Raj Koothrappali. The central romantic storyline begins when Leonard becomes immediately attracted to Penny, an aspiring actress and waitress who moves in across the hall. Throughout the first season, Leonard attempts various schemes to win Penny's affection while she dates a series of conventionally attractive but intellectually incompatible men.
The group's friendship dynamics are established as they navigate their shared interests in science fiction, comic books, and video games, often clashing with their limited social skills. Sheldon's rigid personality and numerous quirks create ongoing conflicts with his roommate Leonard, while Howard's inappropriate behavior toward women and his unhealthy relationship with his mother provide additional comedic tension. Raj's selective mutism around women becomes a recurring obstacle to his romantic pursuits.
Leonard and Penny's relationship experiences its first major development when Leonard returns from a three-month Arctic expedition in the season three premiere, leading to their first serious romantic relationship. However, the relationship becomes strained when Leonard prematurely declares his love for Penny, who cannot reciprocate the sentiment. Their subsequent breakup leads Leonard to pursue a relationship with Raj's sister Priya during much of season four, creating tension within the friend group and jealousy from Penny.
Seasons 5–8 The series expands its core cast with the introduction of Amy Farrah Fowler, a neurobiologist matched with Sheldon through online dating, and Bernadette Rostenkowski, a microbiologist who begins dating Howard. These additions create new relationship dynamics and storylines while allowing for character development among the original cast members.
Sheldon and Amy's relationship develops slowly from a purely intellectual connection to a romantic partnership, with Sheldon gradually overcoming his aversion to physical contact and emotional intimacy. Their relationship is marked by formal agreements and scientific approaches to romance, reflecting both characters' analytical personalities.
Howard's relationship with Bernadette leads to significant character growth as he learns to become more mature and less dependent on his mother. Their relationship culminates in marriage during the fifth season finale, coinciding with Howard's departure for a space mission to the International Space Station.
Leonard and Penny reconcile and resume their romantic relationship, though it faces various challenges including Leonard's insecurities and Penny's career struggles. Leonard's multiple attempts to propose marriage are initially rejected by Penny, who feels unprepared for such commitment. The relationship dynamics continue to evolve as both characters mature and better understand each other's needs and perspectives.
Seasons 9–12 The final seasons focus on the progression of established relationships toward marriage and long-term commitment. Leonard and Penny finally marry in the season nine premiere, though their wedding is preceded by Leonard's confession of kissing a co-worker during his Arctic expedition. Despite this obstacle, they successfully navigate married life and eventually move into their own apartment when Sheldon relocates.
Sheldon and Amy's relationship reaches several major milestones, including their first sexual encounter on Amy's birthday and eventual cohabitation. After a temporary breakup caused by Sheldon's fear of commitment, they reunite and become engaged. Their wedding in the season eleven finale represents the culmination of Sheldon's character development from an emotionally closed individual to someone capable of love and partnership.
The series concludes with the characters achieving personal and professional fulfillment. The final episode reveals Penny's pregnancy while focusing on Sheldon and Amy receiving the Nobel Prize in Physics, bringing the characters' scientific careers full circle while emphasizing the importance of their personal relationships and friendships that have sustained them throughout the series.
Cast and characters
Johnny Galecki as Leonard Hofstadter: An experimental physicist with an IQ of 173, who received his Ph.D. when he was 24 years old. Leonard is a nerd who loves video games, comic books, and Dungeons & Dragons. Leonard is the straight man of the series, sharing an apartment in Pasadena, CA, with Sheldon Cooper. Leonard is smitten upon meeting his new neighbor, Penny, and they eventually marry. Jim Parsons as Sheldon Cooper: Originally from Galveston, Texas, Sheldon was a child prodigy with an eidetic memory who began college at the age of eleven and earned a Ph.D. at age sixteen. He is a theoretical physicist researching quantum mechanics and string theory, and, despite his IQ of 187, he finds many routine aspects of social situations difficult to grasp. He is determined to have his own way, continually boasts of his intelligence, and has an extremely ritualized way of living. Despite these quirks, he begins a relationship with Amy Farrah Fowler, and they eventually marry. Kaley Cuoco as Penny: An aspiring actress from Omaha, Nebraska. Penny moves in across the hall from Sheldon and Leonard. She waits tables and occasionally tends the bar at The Cheesecake Factory. After giving up hope of becoming a successful actress, Penny becomes a pharmaceutical sales representative. Penny becomes friends with Bernadette and Amy, and they often hang out in each other's apartments. Penny and Leonard form a relationship and eventually marry. Simon Helberg as Howard Wolowitz: An aerospace engineer who got his master's degree at the Massachusetts Institute of Technology. Howard is Jewish and lived with his mother, Debbie (Carol Ann Susi). Unlike Sheldon, Leonard, Raj, Bernadette, and Amy, Howard does not hold a doctorate. He trains as an astronaut and goes into space as a payload specialist on the International Space Station. Howard initially fancies himself as a ladies man, but he later starts dating Bernadette, and they get engaged and married. Howard also has a tendency to waste money on toys and argues with Bernadette because of his oddly low income as an engineer and her high income as a pharmaceutical biochemist. Kunal Nayyar as Rajesh "Raj" Koothrappali: A particle astrophysicist originally from New Delhi, India. Initially, Raj had selective mutism, rendering him unable to talk to or be around women unless under the influence of alcohol. Raj also has very feminine tastes and often takes on a stereotypical female role in his friendship with Howard as well as in the group of four men. Raj later dates Lucy (Kate Micucci), who also suffers from social anxiety, but it eventually ends. He later speaks to Penny without alcohol, overcoming his selective mutism. He begins dating Emily Sweeney, and their relationship later becomes exclusive. In the series' final season, Raj has an on-again, off-again engagement with a hotel concierge named Anu (Rati Gupta). He also has a Yorkshire Terrier named Cinnamon, given by Howard and Bernadette. Melissa Rauch as Bernadette Rostenkowski-Wolowitz (recurring season 3, starring seasons 412): A young woman who initially is a co-worker at The Cheesecake Factory with Penny to pay her way through graduate school, where she is studying microbiology. Bernadette is introduced to Howard by Penny; at first, they do not get along, apparently having nothing in common. They date and later get engaged, married, and had 2 kids. Although generally a sweet and good-natured person, Bernadette has a short fuse and can be vindictive and lash out when provoked. Mayim Bialik as Amy Farrah Fowler (guest star season 3, starring seasons 412): A woman selected by an online dating site as Sheldon's perfect mate, Amy is from Glendale, California. While she and Sheldon initially share social cluelessness, after befriending Penny and Bernadette, she eventually becomes more interested in social and romantic interaction. Her relationship with Sheldon slowly progresses to the point where Sheldon considers her his girlfriend, and eventually, they get married. Amy believes she and Penny are best friends, a sentiment that Penny does not initially share. Amy has a Ph.D. in neurobiology. Kevin Sussman as Stuart Bloom (recurring seasons 25, 7, starring seasons 6, 812): A mild-mannered, under-confident owner of a comic book store. A competent artist, Stuart is a graduate of the prestigious Rhode Island School of Design. Though he is socially awkward, he possesses slightly better social skills. Stuart implies he is in financial trouble and that the comic book store now also is his home. He is later invited to join the guys' group while Howard is in space. Stuart gets a new job caring for Howard's mother later. After Mrs. Wolowitz's death, Stuart continues to live in her home, along with Howard and Bernadette, until he finds a place of his own. Laura Spencer as Emily Sweeney (recurring seasons 78, 10, starring season 9): A dermatologist at Huntington Hospital. Emily went to Harvard and delights in the macabre, and she states that she likes her job because she can cut things with knives. Prior to meeting Raj, Emily was set up on a blind date with Howard. After finding Emily's online dating profile, Raj has Amy contact her as his wingman instead. Their relationship becomes exclusive, but Raj later breaks up with Emily when he becomes infatuated with Claire (Alessandra Torresani), a bartender and children's author.