Penny's Posse is the subgroup of the Social Group made up of the female members, Penny, Bernadette and Amy. They are the female halves of the relationships that have developed for the male members, Leonard, Sheldon, Howard and Raj, though Raj's girlfriend Emily doesn't hangout with just the girls. The original show dynamics were how the new girl Penny affects the lives of the male members and specifically Leonard's interest and pursuit of Penny.During season 4, Howard established Bernadette as his permanent girlfriend and Amy became Sheldon's friend who was a girl, but not his girlfriend the Posse began. Bernadette was friends with Penny from working at The Cheesecake Factory together and Amy push herself toward Penny claiming her as her best and only friend. Their first night of hanging out together was in "The 21-Second Excitation" while the guys were waiting in line for a re-release of "Raiders of the Lost Ark". Amy was awkward with her interactions with the other two and creeped them out a bit, but gradually they accepted each other an became friends. Penny introduced Amy to new experiences like shopping .together, alcohol, trash talking and the emotional aspects of male-female relationships. The latter experience changed her relationship with Sheldon from her acting just like him to adding experiencing sexual arousal, hand holding, becoming a girlfriend, kissing and to date both Amy and Sheldon telling them that they loved each other. Another strong influence in the Posse was Bernadette choosing Amy for the maid of honor at her wedding after she was hurt when they didn't go dress shopping together. Amy is not against suggesting things that she reads off the internet that women friends do or comforting Penny in a crisis and using her as a subject in her experiments. She also has a limited attraction to Penny and thinks that Bernadette is the least cool of the Posse; however by seasons 7 and 8 she has bonded closer with Bernadette since they are fellow scientists. Using the Posse, some episodes have the story lines split down the middle between males and females as they guys follow nerdy pursuit as they have all their lives and the girls hang out in Penny's apartment or have a girls' nights out. The storylines have become much more complicated with parallel plots after the additional of new cast members. They also play hooky and go to Disneyland together and get makeovers as Disney princesses. Most of the time they are hanging out in Penny's apartment, but they have gone to bars, restaurants, a tea parlor, strip clubs and a trip to Las Vegas together. The girls have a habit of helping both Sheldon with problems with life and Raj and his love life after he loses his selective mutism.
- The only episode in the entire show that all three members of the group (Penny, Bernadette and Amy) did not get featured in for any appearances was the Season 4 episode of "The Irish Pub Formulation" (S4E6).
- Bernadette and Amy are the only members of the group that did not get dressed up as a comic superhero as of them not featuring in the episode of "The Justice League Recombination" (S4E11) to which were not required for the storylines in that episode.
- Penny is the only member of the group to have her belly button seen on-camera and seen in a bikini while Bernadette and Amy are the only members of the group that haven't been seen in a bikini or have their belly buttons seen on-camera because they were too hung over to get off the bed and come to the pool with Penny at the end of "The Focus Attenuation" (S8E5) whilst vacationing in Vegas.
- Whereas some episodes with different numerous non-Big Bang Theory actress doing bikini scenes (like sunbathing on a balcony etc.) and having a belly button seen on-camera were usually shown in the beach house by the sea comedy show with Charlie Sheen (aka Charlie Harper who has a lot of girls) called "Two and a Half Men" (which was also by Chuck Lorre productions).
- Every member of the group has been seen topless in some episodes.
- Amy has been seen topless for the first time in bed with Sheldon and with her glasses off in "The Opening Night Excitation" (S9E11).
- Bernadette had been topless in bed with Howard in two scenes of "The Cohabitation Formulation" (S4E16), the ending scene of "The Expedition Approximation" (S8E6) and a scene of "The Sales Call Sublimation" (S9E12). She was also seen with her glasses off while she was topless in bed as well.
- Penny had been seen topless in numerous episode scenes (like showering, having sex with Leonard and so on) in the entire show.
- Bernadette and Amy are the only members of the group not to be seen in their underwear since the time Amy accidentally filmed Penny in her underwear during the last shot of the ending scene with wedding dress fitting in the episode of "The Isolation Permutation" (S5E8) and a bit of her underwear could be seen under her nightie in "The Raiders Minimization" (S7E4).
- Penny was the only member of the group to have a bra shot in a few episodes of the entire show whilst Bernadette and Amy never had any bra shots in any episodes of the entire show. Penny is the only member to have a belly button seen on-camera with her bra shots in one of the dream sequences of "The Cooper Extraction" (S7E11) whereas Bernadette and Amy never had any bra shots and belly buttons seen on-camera.
- Bernadette was the only member in the group who hadn't been seen with Sheldon's mother for long until "The Conjugal Conjecture" (S10E01), but didn't talk.
- Penny is the only member who isn't bespectacled (not including the one instance where she wore glasses at the end of "The Egg Salad Equivalency").
- Bernadette and Amy were the only members in the group who hadn't been seen with Leonard's mother for long until "The Celebration Experimentation" (S9E17) but didn't talk. However, in "The Line Substitution Solution" (S9E23), they were seen with her again and for the first time she had conversations with them.
- Bernadette is the only gang member in the group who has never met Alex Jensen whereas only Penny and Amy have.