The Electric Can Opener Fluctuation: Leonard's attempts to woo Penny are constantly thwarted. Sheldon heads to Texas after learning his friends meddled with his expedition data. (S3 Ep1) [AD,S]
The Jiminy Conjecture: Leonard and Penny feel awkward around each other after their romantic liaison, while Sheldon and Howard take bets to determine a species of cricket. (S3 Ep2) [AD,S]
The Ornithophobia Diffusion: Leonard and Penny attempt to spend time together as friends without anybody else around, while Sheldon faces his fear of birds. (S5 Ep9) [AD,S]
The Flaming Spittoon Acquisition: Stuart from the comic book shop invites Amy out on a date. Consumed by jealousy, Sheldon then asks her to be his girlfriend. (S5 Ep10) [AD,S]
The Speckerman Recurrence: Leonard confronts the man who bullied him in high school, while Penny realises that she did her fair share of tormenting in the past. (S5 Ep11) [AD,S]
The Shiny Trinket Maneuver: When Sheldon is dismissive of Amy's career, Penny, Raj and Leonard teach him that sometimes it's a good idea to pretend to care about things. (S5 Ep12) [AD,S]
The Recombination Hypothesis: In the 100th episode of the US sitcom, Leonard and Penny agree to give their relationship another chance, but they soon start to argue again. (S5 Ep13) [AD,S]
The Vacation Solution: Sheldon helps Amy in her biology lab after he is forced to use up two weeks of holiday, but he is bored by the tasks that she gives him. (S5 Ep16) [AD,S]
The Beta Test Initiation: Leonard and Penny put their relationship through a 'beta test' and report problems with each other as 'bugs'. Sheldon and Amy seek internet fame. (S5 Ep14) [AD,S]
The Locomotion Interruption: Leonard and Amy take an impromptu road trip to Arizona to pick up Sheldon when his epic railway journey ends in chaos. Penny has an interview. (S8 Ep1) [AD,S]
The Junior Professor Solution: When Sheldon has to teach a course at the university, Howard enrols in his class. Tension brews between Penny and Bernadette. (S8 Ep2) [AD,S]
The Locomotion Interruption: Leonard and Amy take an impromptu road trip to Arizona to pick up Sheldon when his epic railway journey ends in chaos. Penny has an interview. (S8 Ep1) [AD,S]
The Junior Professor Solution: When Sheldon has to teach a course at the university, Howard enrols in his class. Tension brews between Penny and Bernadette. (S8 Ep2) [AD,S]
The Skank Reflex Analysis: Penny worries that she's screwed things up with her friends after her night with Raj. Sheldon takes command of the paintball team. (S5 Ep1) [AD,S]
The Infestation Hypothesis: Amy is stuck in the middle of a battle of wills between Penny and Sheldon. Leonard and Priya try to spice up their long-distance relationship. (S5 Ep2) [AD,S]
The Pulled Groin Extrapolation: Leonard goes to a colleague's wedding as Amy's date. Howard tries to convince Bernadette to live with his mum after they get married. (S5 Ep3) [AD,S]
The Skank Reflex Analysis: Penny worries that she's screwed things up with her friends after her night with Raj. Sheldon takes command of the paintball team. (S5 Ep1) [AD,S]
The Wiggly Finger Catalyst: Raj begins to get upset that he's the only one of the four guys not in a relationship, so Penny sets out to find him the perfect date. (S5 Ep4) [AD,S,SL]
The Infestation Hypothesis: Amy is stuck in the middle of a battle of wills between Penny and Sheldon. Leonard and Priya try to spice up their long-distance relationship. (S5 Ep2) [AD,S]
The Pulled Groin Extrapolation: Leonard goes to a colleague's wedding as Amy's date. Howard tries to convince Bernadette to live with his mum after they get married. (S5 Ep3) [AD,S]
The Wiggly Finger Catalyst: Raj begins to get upset that he's the only one of the four guys not in a relationship, so Penny sets out to find him the perfect date. (S5 Ep4) [AD,S,SL]
The Date Night Variable: Howard gets caught in a row between his mum and Bernadette while he's at the International Space Station. Sheldon invites Raj along on a date with Amy. (S6 Ep1) [AD,S]
The Decoupling Fluctuation: Sheldon intervenes when he learns that Penny is thinking about breaking up with Leonard, but he's hampered by his inability to keep a secret. (S6 Ep2) [AD,S]
The Higgs Boson Observation: Amy is jealous when Sheldon hires an attractive female assistant, and Howard's return from space is delayed by a week. (S6 Ep3) [AD,S]
The Date Night Variable: Howard gets caught in a row between his mum and Bernadette while he's at the International Space Station. Sheldon invites Raj along on a date with Amy. (S6 Ep1) [AD,S]
The Re-entry Minimization: Howard is disappointed when he doesn't receive a hero's welcome on his return from space. Will he ever get the recognition he deserves? (S6 Ep4) [AD,S]
The Decoupling Fluctuation: Sheldon intervenes when he learns that Penny is thinking about breaking up with Leonard, but he's hampered by his inability to keep a secret. (S6 Ep2) [AD,S]
The Holographic Excitation: The gang celebrate Halloween with a fancy dress party at Stuart's comic book shop, but Sheldon and Amy can't agree on which costumes to wear. (S6 Ep5) [AD,S]
The Higgs Boson Observation: Amy is jealous when Sheldon hires an attractive female assistant, and Howard's return from space is delayed by a week. (S6 Ep3) [AD,S]
The Extract Obliteration: Sheldon is thrilled when Stephen Hawking agrees to play against him in an online game. Penny signs up for a class at the community college. (S6 Ep6) [AD,S]
The Re-entry Minimization: Howard is disappointed when he doesn't receive a hero's welcome on his return from space. Will he ever get the recognition he deserves? (S6 Ep4) [AD,S]
The Habitation Configuration: Amy is upset when Sheldon fails to defend her in an argument with Wil Wheaton during the filming of a new episode of Fun with Flags. (S6 Ep7) [AD,S]
The Holographic Excitation: The gang celebrate Halloween with a fancy dress party at Stuart's comic book shop, but Sheldon and Amy can't agree on which costumes to wear. (S6 Ep5) [AD,S]
The 43 Peculiarity: The guys notice that Sheldon disappears for 20 minutes after lunch every day. Filled with curiosity, they attempt to work out what he's been doing. (S6 Ep8) [AD,S]
The Extract Obliteration: Sheldon is thrilled when Stephen Hawking agrees to play against him in an online game. Penny signs up for a class at the community college. (S6 Ep6) [AD,S]
The Parking Spot Escalation: When non-driver Sheldon finds out that his unused parking space at the university has been reallocated to Howard, he feels undermined. (S6 Ep9) [AD,S]
The Habitation Configuration: Amy is upset when Sheldon fails to defend her in an argument with Wil Wheaton during the filming of a new episode of Fun with Flags. (S6 Ep7) [AD,S]
The Fish Guts Displacement: Sheldon begrudgingly takes care of Amy when she is sick. Bernadette arranges for Howard to go on a fishing trip with her macho father. (S6 Ep10) [AD,S]
The 43 Peculiarity: The guys notice that Sheldon disappears for 20 minutes after lunch every day. Filled with curiosity, they attempt to work out what he's been doing. (S6 Ep8) [AD,S]
The Santa Simulation: Sheldon unwillingly reveals painful memories of Christmas past when Leonard persuades him to join in with a seasonal game of Dungeons & Dragons. (S6 Ep11) [AD,S]
The Parking Spot Escalation: When non-driver Sheldon finds out that his unused parking space at the university has been reallocated to Howard, he feels undermined. (S6 Ep9) [AD,S]
The Egg Salad Equivalency: Sheldon is accused of sexual harassment and sent to Human Resources, where he ends up dragging Leonard, Raj and Howard into trouble too. (S6 Ep12) [AD,S]
The Fish Guts Displacement: Sheldon begrudgingly takes care of Amy when she is sick. Bernadette arranges for Howard to go on a fishing trip with her macho father. (S6 Ep10) [AD,S]
The Bakersfield Expedition: The guys get all dressed up for a photo opportunity at a Star Trek location but end up stranded in the desert. (S6 Ep13) [AD,S]
The Santa Simulation: Sheldon unwillingly reveals painful memories of Christmas past when Leonard persuades him to join in with a seasonal game of Dungeons & Dragons. (S6 Ep11) [AD,S]
The Cooper/Kripke Inversion: Sheldon is forced to work on the same project as his nemesis, Barry Kripke. Howard and Raj spend a fortune on personalised action figures. (S6 Ep14) [AD,S]
The Egg Salad Equivalency: Sheldon is accused of sexual harassment and sent to Human Resources, where he ends up dragging Leonard, Raj and Howard into trouble too. (S6 Ep12) [AD,S]
The Spoiler Alert Segmentation: After Sheldon and Leonard have a row, Leonard attempts to move in with Penny, even though she isn't ready for such a big step. (S6 Ep15) [AD,S]
The Bakersfield Expedition: The guys get all dressed up for a photo opportunity at a Star Trek location but end up stranded in the desert. (S6 Ep13) [AD,S]
The Tangible Affection Proof: Annoyed at being forced to celebrate Valentine's Day when he hates it, Sheldon delegates the task of buying Amy's gift to his assistant. (S6 Ep16) [AD,S]
The Cooper/Kripke Inversion: Sheldon is forced to work on the same project as his nemesis, Barry Kripke. Howard and Raj spend a fortune on personalised action figures. (S6 Ep14) [AD,S]
The Monster Isolation: After a terrible date with Lucy, Raj vows never to leave his flat again. Sheldon asks Penny to help him record a new episode of Fun with Flags. (S6 Ep17) [AD,S]
The Spoiler Alert Segmentation: After Sheldon and Leonard have a row, Leonard attempts to move in with Penny, even though she isn't ready for such a big step. (S6 Ep15) [AD,S]
The Contractual Obligation Implementation: Leonard, Sheldon and Howard are forced to volunteer for a university committee. Raj plans a stress-free date with Lucy. (S6 Ep18) [AD,S]
The Tangible Affection Proof: Annoyed at being forced to celebrate Valentine's Day when he hates it, Sheldon delegates the task of buying Amy's gift to his assistant. (S6 Ep16) [AD,S]
The Closet Reconfiguration: When Howard and Bernadette get Sheldon to organise their untidy closet, Sheldon finds an unopened letter from Howard's long-absent father. (S6 Ep19) [AD,S]
The Monster Isolation: After a terrible date with Lucy, Raj vows never to leave his flat again. Sheldon asks Penny to help him record a new episode of Fun with Flags. (S6 Ep17) [AD,S]
The Contractual Obligation Implementation: Leonard, Sheldon and Howard are forced to volunteer for a university committee. Raj plans a stress-free date with Lucy. (S6 Ep18) [AD,S]
The Closure Alternative: Amy employs a series of exercises to cure Sheldon of his compulsion to complete every task without fail and seek closure for every incident. (S6 Ep21) [AD,S]
The Closet Reconfiguration: When Howard and Bernadette get Sheldon to organise their untidy closet, Sheldon finds an unopened letter from Howard's long-absent father. (S6 Ep19) [AD,S]
The Proton Resurgence: Leonard and Sheldon hire Professor Proton, the host of a TV science show they watched as children, to come to their flat and entertain them. (S6 Ep22) [AD,S]
The Love Spell Potential: When the girls' trip to Las Vegas falls through, the guys invite them to a Dungeons & Dragons night that changes Sheldon and Amy's relationship. (S6 Ep23) [AD,S]
The Closure Alternative: Amy employs a series of exercises to cure Sheldon of his compulsion to complete every task without fail and seek closure for every incident. (S6 Ep21) [AD,S]
The Bon Voyage Reaction: Leonard is offered an exciting job opportunity that will keep him out of the country for several months. Raj pushes the boundaries of his relationship. (S6 Ep24) [AD,S]
The Proton Resurgence: Leonard and Sheldon hire Professor Proton, the host of a TV science show they watched as children, to come to their flat and entertain them. (S6 Ep22) [AD,S]
The Hofstadter Insufficiency: Sheldon and Penny bond while Leonard is away. Raj finds someone to share his heartache. Bernadette and Amy attract male attention at a conference. (S7 Ep1) [AD,S]
The Love Spell Potential: When the girls' trip to Las Vegas falls through, the guys invite them to a Dungeons & Dragons night that changes Sheldon and Amy's relationship. (S6 Ep23) [AD,S]
The Bon Voyage Reaction: Leonard is offered an exciting job opportunity that will keep him out of the country for several months. Raj pushes the boundaries of his relationship. (S6 Ep24) [AD,S]
The Gothowitz Deviation: Sheldon tries to modify Penny's behaviour, and rewards her with chocolate when she does what he wants, while Howard and Raj go to a goth nightclub. (S3 Ep3) [AD,S]
The Hofstadter Insufficiency: Sheldon and Penny bond while Leonard is away. Raj finds someone to share his heartache. Bernadette and Amy attract male attention at a conference. (S7 Ep1) [AD,S]
The Pirate Solution: Raj must find a job or he'll be sent back to India, so he accepts an offer of work from Sheldon. Leonard and Penny try to get some time for themselves. (S3 Ep4) [AD,S]
The Creepy Candy Coating Corollary: Due to a childhood snub, Sheldon is irked when Star Trek actor Wil Wheaton (guest starring as himself) takes part in the same contest as him. (S3 Ep5) [AD,S]
The Cornhusker Vortex: Sheldon teaches Leonard about American football so that he can try to fit in with Penny's friends. And Raj and Sheldon have a kite-fighting contest. (S3 Ep6) [AD,S]
The Guitarist Amplification: Sheldon is annoyed when Leonard and Penny argue about Penny's male friend staying over and he has to act as peacemaker. (S3 Ep7) [AD,S]
The Adhesive Duck Deficiency: Leonard, Raj and Howard go on a camping trip that alters their minds. Penny dislocates her shoulder when she slips in the shower. (S3 Ep8) [AD,S]
The Maternal Congruence: Leonard is horrified when his mother turns up unannounced for a Christmas visit, and then he finds out that Sheldon knew about her divorce before him. (S3 Ep11) [AD,S]
The Bath Item Gift Hypothesis: At Christmas, Leonard's hunky colleague starts dating Penny, while Sheldon's obsession with gift-giving etiquette torments everyone. (S2 Ep11) [AD,S]
The Vartabedian Conundrum: Leonard goes to Penny for help when his relationship with Stephanie takes off faster than he'd like, but will he act on her advice? (S2 Ep10) [AD,S]
The Jiminy Conjecture: Leonard and Penny feel awkward around each other after their romantic liaison, while Sheldon and Howard take bets to determine a species of cricket. (S3 Ep2) [AD,S]
The Electric Can Opener Fluctuation: Leonard's attempts to woo Penny are constantly thwarted. Sheldon heads to Texas after learning his friends meddled with his expedition data. (S3 Ep1) [AD,S]
The Monopolar Expedition: Leonard and Penny reconsider their feelings for each other, but then Leonard is offered the opportunity to spend the summer working at the North Pole. (S2 Ep23) [AD,S]
The Classified Materials Turbulence: Things look up for Leonard when Penny makes a surprising revelation on her second date with Stuart. Howard sees a flaw in his NASA project. (S2 Ep22) [AD,S]
The Euclid Alternative: When Leonard can't drive Sheldon to and from work, the friends stage an intervention to overcome Sheldon's fear of getting behind the wheel. (S2 Ep5) [AD,S]
The Vegas Renormalization: Leonard and Raj take a heartbroken Howard to Las Vegas, leaving Sheldon locked out of his flat and forced to stay with Penny. (S2 Ep21) [AD,S]
The Hofstadter Isotope: Leonard is devastated when Stuart from the comic book shop chats up Penny. Even worse, she doesn't mind. Sheldon tries to scupper the budding romance. (S2 Ep20) [AD,S]
The Barbarian Sublimation: Penny becomes addicted to an online game based on the world of Conan the Barbarian and begins to pester Sheldon for advice. (S2 Ep3) [AD,S]
The Codpiece Topology: Seeing Penny out on a date with another guy sends a distressed Leonard rushing back to Leslie Winkle, much to Sheldon's dismay. (S2 Ep2) [AD,S]
The Bad Fish Paradigm: Penny opens up to a reluctant Sheldon after a less-than-stellar first date with Leonard, putting him in the awkward position of having to keep a secret. (S2 Ep1) [AD,S]
The Tangerine Factor: When Penny breaks up with her boyfriend, Leonard plucks up the courage to ask her out. And each of them turns to Sheldon for advice about their date. (S1 Ep17) [AD,S]
The Friendship Algorithm: Sheldon develops a scientific procedure for making friends when he discovers that Kripke has control of a new supercomputer at the university. (S2 Ep13) [AD,S]
The Killer Robot Instability: Kripke challenges the boys to a robot duel, while Howard is devastated when Penny finally tells him what she thinks of his chauvinism. (S2 Ep12) [AD,S]
The Bath Item Gift Hypothesis: At Christmas, Leonard's hunky colleague starts dating Penny, while Sheldon's obsession with gift-giving etiquette torments everyone. (S2 Ep11) [AD,S]
The Vartabedian Conundrum: Leonard goes to Penny for help when his relationship with Stephanie takes off faster than he'd like, but will he act on her advice? (S2 Ep10) [AD,S]
The Peanut Reaction: Penny throws a surprise party for Leonard, with help from Howard and Raj, but Sheldon's indulgence in an electronics shop throws her off track. (S1 Ep16) [AD,S]
The Shiksa Indeterminacy: Leonard, Raj and Howard all fall heavily for Sheldon's twin sister, but when Leonard comes up with a plan to win her heart, it's derailed by Sheldon. (S1 Ep15) [AD,S]
The White Asparagus Triangulation: Sheldon is delighted that Leonard has finally found a girlfriend who matches up to his high standards... Perhaps a little too delighted. (S2 Ep9) [AD,S]
The Panty PiÄnata Polarization: Sheldon bans Penny from the flat for numerous minor infractions, so she retaliates. Howard and Raj search for the America's Next Top Model house. (S2 Ep7) [AD,S]
The Cooper-Nowitzki Theorem: Sheldon's friends are mystified when a younger student is attracted to him, and her intense devotion soon becomes too much to bear. (S2 Ep6) [AD,S]
The Loobenfeld Decay: Leonard and Sheldon each tell a lie to avoid going to see Penny singing on stage in a production of Rent, but Sheldon's fib gets out of control. (S1 Ep10) [AD,S]
The Cooper-Hofstadter Polarization: Sheldon and Leonard fall out when they're asked to collaborate at a physics conference. Penny tries to help but just makes things worse. (S1 Ep9) [AD,S]
The Grasshopper Experiment: Raj panics when his parents arrange a blind date for him. But he discovers that he can talk to her - after a few drinks. (S1 Ep8) [AD,S]
The Dumpling Paradox: When Howard seduces Penny's friend and spends the night with her in Penny's flat, Penny asks if she can sleep on Leonard and Sheldon's sofa. (S1 Ep7) [AD,S]
The Middle Earth Paradigm: Penny's Halloween party puts Leonard, Sheldon, Howard and Raj through a demanding new test of their social skills. (S1 Ep6) [AD,S]
The Hamburger Postulate: Leonard thinks he's been wasting his time on Penny, so he turns his attention to Leslie. Sheldon's uncomfortable with a change to his hamburger routine. (S1 Ep5) [AD,S]
The Luminous Fish Effect: Getting fired forces Sheldon to ponder life outside physics, so Leonard has to take drastic action to snap his friend out of his reverie. (S1 Ep4) [AD,S]
The Fuzzyboots Corollary: Leonard is upset when he discovers that Penny is seeing someone, so he plucks up the courage to ask a woman out on a date. (S1 Ep3) [AD,S]
The Euclid Alternative: When Leonard can't drive Sheldon to and from work, the friends stage an intervention to overcome Sheldon's fear of getting behind the wheel. (S2 Ep5) [AD,S]
The Griffin Equivalency: Full of confidence after being named one of People magazine's '30 to Watch Under 30', Raj hits on Penny and becomes impossibly arrogant. (S2 Ep4) [AD,S]
The Barbarian Sublimation: Penny becomes addicted to an online game based on the world of Conan the Barbarian and begins to pester Sheldon for advice. (S2 Ep3) [AD,S]
The Codpiece Topology: Seeing Penny out on a date with another guy sends a distressed Leonard rushing back to Leslie Winkle, much to Sheldon's dismay. (S2 Ep2) [AD,S]
Pilot: The first ever episode of the hit sitcom. Leonard and Sheldon's geeky world is shaken up by the arrival of a beautiful new neighbour. (S1 Ep1) [AD,S]
The Bad Fish Paradigm: Penny opens up to a reluctant Sheldon after a less-than-stellar first date with Leonard, putting him in the awkward position of having to keep a secret. (S2 Ep1) [AD,S]
The Tangerine Factor: When Penny breaks up with her boyfriend, Leonard plucks up the courage to ask her out. And each of them turns to Sheldon for advice about their date. (S1 Ep17) [AD,S]
The Peanut Reaction: Penny throws a surprise party for Leonard, with help from Howard and Raj, but Sheldon's indulgence in an electronics shop throws her off track. (S1 Ep16) [AD,S]
The Shiksa Indeterminacy: Leonard, Raj and Howard all fall heavily for Sheldon's twin sister, but when Leonard comes up with a plan to win her heart, it's derailed by Sheldon. (S1 Ep15) [AD,S]
The Stockholm Syndrome: Howard and Bernadette go on a trip without their children, Leonard and Penny try to keep a secret, and Raj makes a new friend. (S12 Ep24) [AD,S]
The Change Constant: Sheldon and Amy stay up late awaiting a phone call that could bring big news from the Nobel Committee: are their lives about to change? (S12 Ep23) [AD,S]
The Nerdvana Annihilation: When Penny makes fun of Leonard's habit of collecting goofy memorabilia, his friends kick up a fuss and try to keep him on the side of the nerds. (S1 Ep14) [AD,S]
The Bat Jar Conjecture: Sheldon is ousted from the gang's Physics Bowl quiz team, so he decides to prove his superiority by forming his own team for the event. (S1 Ep13) [AD,S]
The Pancake Batter Anomaly: Penny volunteers to nurse Sheldon when he's sick. But his friends, who know how miserable he is when he's ill, stay well away. (S1 Ep11) [AD,S]
The Maternal Conclusion: Leonard is surprised when his mother Beverly comes to visit and is kind to him, until he finds out the real reason she's there. (S12 Ep22) [AD,S]
The Plagiarism Schism: Barry Kripke finds proof that Dr Pemberton plagiarised his thesis in college. Should Sheldon and Amy turn in their rival? (S12 Ep21) [AD,S]
The Loobenfeld Decay: Leonard and Sheldon each tell a lie to avoid going to see Penny singing on stage in a production of Rent, but Sheldon's fib gets out of control. (S1 Ep10) [AD,S]