Series 9 Episode 17
After more than nine years together, the gang finally manage to persuade a reluctant Sheldon to celebrate his birthday, so they throw him a party with a few special guests in the 200th episode
Series 9 Episode 1
The Matrimonial Momentum: After driving all the way to Las Vegas for her wedding to Leonard, Penny faces a dilemma
Series 9 Episode 1
Series 9 Episode 2
The Separation Oscillation: Leonard tries to put Penny's mind at ease about their relationship
Series 9 Episode 2
Series 9 Episode 3
The Bachelor Party Corrosion: The guys get a flat tyre during Leonard's surprise bachelor party weekend in Mexico
Series 9 Episode 3
Series 9 Episode 4
The 2003 Approximation: Sheldon decides to revisit 2003, a simpler time before he had met either Penny or Leonard
Series 9 Episode 4
Series 9 Episode 5
The Perspiration Implementation: The guys take fencing lessons from Barry Kripke, who expresses a romantic interest in Amy
Series 9 Episode 5
Series 9 Episode 6
The Helium Insufficiency: Sheldon and Leonard struggle to find the supplies they need for a scientific experiment
Series 9 Episode 6
Series 9 Episode 7
The Spock Resonance: While being interviewed for a documentary, Sheldon can't suppress his emotions about Amy
Series 9 Episode 7
Series 9 Episode 8
The Mystery Date Observation: Sheldon enlists the help of Howard and Raj to find him a new girlfriend by posting online
Series 9 Episode 8
Series 9 Episode 9
The Platonic Permutation: Sheldon and Amy try hanging out as friends when they spend Thanksgiving at the aquarium
Series 9 Episode 9
Series 9 Episode 10
The Earworm Reverberation: Sheldon is driven to distraction when he can't get a familiar tune out of his head
Series 9 Episode 10
Series 9 Episode 11
The Opening Night Excitation: Sheldon seeks advice from Penny and Bernadette while planning a treat for Amy's birthday
Series 9 Episode 11
Series 9 Episode 12
The Sales Call Sublimation: Penny gets more than she bargained for when Leonard meets a psychiatrist
Series 9 Episode 12
Series 9 Episode 13
The Empathy Optimization: The gang decide to treat themselves to a Sheldon-free weekend in Las Vegas
Series 9 Episode 13
Series 9 Episode 14
The Meemaw Materialization: Sheldon is thrilled when his grandmother comes to visit, but she soon butts heads with Amy
Series 9 Episode 14
Series 9 Episode 15
The Valentino Submergence: Sheldon and Amy host a live Valentine's Day episode of their internet show Fun with Flags
Series 9 Episode 15
Series 9 Episode 16
The Positive Negative Reaction: When the gang hear about Bernadette's big news, they celebrate with an evening of karaoke
Series 9 Episode 16
Series 9 Episode 17
The Celebration Experimentation: The gang persuade Sheldon to celebrate his birthday with a party in the 200th episode
Series 9 Episode 17
Series 9 Episode 18
The Application Deterioration: Raj needs some relationship advice when Emily reaches out to him after their break-up
Series 9 Episode 18
Series 9 Episode 19
The Solder Excursion Diversion: Sheldon makes a revelation when Amy buys him a new laptop. Leonard and Howard tell a lie.
Series 9 Episode 19
Series 9 Episode 20
The Big Bear Precipitation: Sheldon shares a big secret about Leonard during a weekend trip to a cabin in the country
Series 9 Episode 20