The Big Bang Theory

Penny hosts a Halloween costume party, which proves the ideal opportunity for the boys to test their social skills. Kaley Cuoco and Johnny Galecki star

Penny is forced to take Howard's place in the boys' video-game night while he is otherwise engaged with one of her friends. Starring Simon Helberg and Kaley Cuoco

Raj's parents set him up on a blind date in the hope of initiating an arranged marriage, but the girl in question seems more interested in Sheldon

Leonard and Sheldon receive an invitation to present their research to a physics conference, but it causes conflict between them - and Penny's intervention makes matters worse

Sheldon and Leonard invent excuses to avoid going to watch Penny's performance in a musical, but maintaining the pretence makes matters ever more complicated

Sheldon falls ill and his friends stay well away, knowing he will be in a terrible mood, but an unsuspecting Penny offers to nurse him

Sheldon feels threatened by a 15-year-old physics prodigy who is even cleverer than he is, and asks Leonard to help him discredit the teenager's research

Penny is forced to take Howard's place in the boys' video-game night while he is otherwise engaged with one of her friends. Starring Simon Helberg and Kaley Cuoco

Raj's parents set him up on a blind date in the hope of initiating an arranged marriage, but the girl in question seems more interested in Sheldon

Leonard and Sheldon receive an invitation to present their research to a physics conference, but it causes conflict between them - and Penny's intervention makes matters worse

Penny is forced to take Howard's place in the boys' video-game night while he is otherwise engaged with one of her friends. Starring Simon Helberg and Kaley Cuoco

Sheldon and Leonard invent excuses to avoid going to watch Penny's performance in a musical, but maintaining the pretence makes matters ever more complicated

Raj's parents set him up on a blind date in the hope of initiating an arranged marriage, but the girl in question seems more interested in Sheldon

Leonard and Sheldon receive an invitation to present their research to a physics conference, but it causes conflict between them - and Penny's intervention makes matters worse

Sheldon and Leonard invent excuses to avoid going to watch Penny's performance in a musical, but maintaining the pretence makes matters ever more complicated

Penny is forced to take Howard's place in the boys' video-game night while he is otherwise engaged with one of her friends. Starring Simon Helberg and Kaley Cuoco

Raj's parents set him up on a blind date in the hope of initiating an arranged marriage, but the girl in question seems more interested in Sheldon

Leonard and Sheldon receive an invitation to present their research to a physics conference, but it causes conflict between them - and Penny's intervention makes matters worse

Penny is forced to take Howard's place in the boys' video-game night while he is otherwise engaged with one of her friends. Starring Simon Helberg and Kaley Cuoco

Sheldon pushes himself to the limit when he commits to two projects - one with Leonard and Howard, the other with Amy - on the same day. Bernadette prepares to return to work

Raj's parents set him up on a blind date in the hope of initiating an arranged marriage, but the girl in question seems more interested in Sheldon

Howard and Bernadette find it upsetting to leave their daughter at the nursery, while the gang's university pal Bert the geologist introduces them to his attractive new girlfriend

Leonard and Sheldon receive an invitation to present their research to a physics conference, but it causes conflict between them - and Penny's intervention makes matters worse

Sheldon pushes himself to the limit when he commits to two projects - one with Leonard and Howard, the other with Amy - on the same day. Bernadette prepares to return to work

Penny considers taking a new job - but Leonard is not thrilled to learn it has been offered to her by her former boyfriend Zack

Howard and Bernadette find it upsetting to leave their daughter at the nursery, while the gang's university pal Bert the geologist introduces them to his attractive new girlfriend

Amy is offered a fellowship at Princeton University, Raj makes new living arrangements, and the guys' infinite persistence gyroscope project spins out of control

Penny considers taking a new job - but Leonard is not thrilled to learn it has been offered to her by her former boyfriend Zack

The gang become concerned when Sheldon's former admirer Dr Ramona Nowitzki resurfaces while Amy is away working at Princeton University. Jim Parsons stars

Amy is offered a fellowship at Princeton University, Raj makes new living arrangements, and the guys' infinite persistence gyroscope project spins out of control

The gang become concerned when Sheldon's former admirer Dr Ramona Nowitzki resurfaces while Amy is away working at Princeton University. Jim Parsons stars

Leonard, Raj and Howard kick Sheldon off their quiz team, so he decides to prove his superiority by forming a rival squad of his own. Johnny Gale and Jim Parsons star

Penny makes fun of Leonard's habit of collecting sci-fi memorabilia, so he decides to give it up - but his friends try to stop him changing his ways

Leonard and Howard send Sheldon on a train journey to keep him away from their Air Force project - but the plan backfires. Bernadette has her first night out since having the baby

Amy is furious with Sheldon for sharing intimate details of their relationship with his friends. Raj considers trying to live without financial support from his father

Leonard and Howard send Sheldon on a train journey to keep him away from their Air Force project - but the plan backfires. Bernadette has her first night out since having the baby

Amy is furious with Sheldon for sharing intimate details of their relationship with his friends. Raj considers trying to live without financial support from his father

Amy is attracted to Penny's former boyfriend Zack, while Raj and Howard compete to prove which of them would make the better superhero

The guys have fun at the expense of Penny's boyfriend Zack, but later try to make amends by enlisting his help with a New Year's costume competition

Amy is attracted to Penny's former boyfriend Zack, while Raj and Howard compete to prove which of them would make the better superhero

Leonard's idea for a smartphone app puts pressure on his friendship with Sheldon, who vies with him for control of the project. Starring Johnny Galecki and Simon Helberg

Tension mounts when the pals attend a weekend science conference and Bernadette runs into a former boyfriend, leaving Howard in an argumentative mood

The guys have fun at the expense of Penny's boyfriend Zack, but later try to make amends by enlisting his help with a New Year's costume competition

Leonard's idea for a smartphone app puts pressure on his friendship with Sheldon, who vies with him for control of the project. Starring Johnny Galecki and Simon Helberg

Tension mounts when the pals attend a weekend science conference and Bernadette runs into a former boyfriend, leaving Howard in an argumentative mood

Sheldon's mother comes to visit and woos the gang, but he cannot help feeling jealous of all the attention she is receiving. Comedy, starring Jim Parsons

Leonard kisses a girl he meets in the comic-book store, while the gang celebrates Halloween by playing pranks on Sheldon. Comedy, starring Johnny Galecki and Jim Parsons

Sheldon's mother comes to visit and woos the gang, but he cannot help feeling jealous of all the attention she is receiving. Comedy, starring Jim Parsons

Amy is hurt to discover Penny and Bernadette went shopping for bridesmaid dresses without her and turns to a reluctant Sheldon for comfort. Comedy, starring Mayim Bialik

Leonard kisses a girl he meets in the comic-book store, while the gang celebrates Halloween by playing pranks on Sheldon. Comedy, starring Johnny Galecki and Jim Parsons

Leonard and Penny endure an awkward night at the cinema, both insisting the outing is not a date. Meanwhile, Sheldon is forced to face his fear of birds

Amy is hurt to discover Penny and Bernadette went shopping for bridesmaid dresses without her and turns to a reluctant Sheldon for comfort. Comedy, starring Mayim Bialik

Leonard and Penny endure an awkward night at the cinema, both insisting the outing is not a date. Meanwhile, Sheldon is forced to face his fear of birds

Sheldon is flattered when a graduate student takes a shine to him, but she soon removes forces him to work on a troublesome scientific problem

Sheldon bans Penny from the apartment for numerous minor infringements, so she decides to retaliate. Howard and Raj search for the America's Next Top Model house

Howard becomes convinced he has met his soulmate in the form of surgeon Stephanie Barnett, but he fails to realise she is far more interested in Leonard. Sara Rue guest stars

Sheldon is delighted that Leonard finally has a girlfriend matching his high standards, but his over-exuberance looks set to cause problems

Sheldon is hurt when Professor Proton contacts Leonard

Leonard worries that Sheldon will overreact when his friend learns about a past indiscretion, while Penny confronts Raj's old flame Lucy

Sheldon is hurt when Professor Proton contacts Leonard

Leonard worries that Sheldon will overreact when his friend learns about a past indiscretion, while Penny confronts Raj's old flame Lucy

Sheldon is hurt when Professor Proton contacts Leonard

Sheldon is hurt when Professor Proton contacts Leonard

Sheldon's friends all fall for his sexy twin sister, who is paying him a visit - but he declares he will have the final say on who can date her

Penny plans to throw a surprise party for Leonard and enlists Sheldon to help with the arrangements, while Howard comes up with an elaborate plan to distract the birthday boy

The gang's annual trip to Comic-Con is thrown into doubt when Raj, who is no longer accepting his father's financial support, cannot afford to go

Leonard and Penny offer Sheldon's old room to Raj, which creates unexpected conflict among everyone and an argument between Amy and Leonard's mother

The gang's annual trip to Comic-Con is thrown into doubt when Raj, who is no longer accepting his father's financial support, cannot afford to go

Leonard and Penny offer Sheldon's old room to Raj, which creates unexpected conflict among everyone and an argument between Amy and Leonard's mother

Sheldon participates in a series of short lectures, but worries about the students' reactions to him, and asks Penny for acting lessons to help him engage with his audience

A wealthy benefactor at the university makes Leonard consider how far he is willing to push himself in the name of science. Comedy, starring Johnny Galecki