A flashback in the season three episode “The Staircase Implementation” reveals that the two characters met when Leonard applied to be Sheldon's roommate. That moment, we are told, was “seven years ago”, and the episode aired in 2010, meaning that Sheldon and Leonard presumably met in 2003.
A Roommate Agreement is a written contract between roommates that outlines their rights and obligations while living together. This agreement includes house rules, maintenance duties, restricted behaviors, and more. For a Roommate Agreement to be useful, everyone sharing the household must agree to it.
A roommate arrangement is when multiple adults occupy a single unit together. In most cases, the renters are not related, but siblings and cousins can be roommates as well. With a traditional roommate arrangement, all roommates share a single lease.
Do Not Use Each Other's Things Without Asking. Not using each other's things without asking is one of the more obvious roommate rules. While some people are more casual about sharing, others are not. You have to learn what kind of person your roommate is and then act ingly.
It dictates what Leonard has to eat each day of the week, what TV shows he is allowed to watch, whether he has a girlfriend stay over, that he has to drive Sheldon everywhere he wishes to go, whenever he wishes. It even dictates when Leonard is allowed to use the bathroom.
The Staircase Implementation - The Big Theory (Season 3, Episode 22) - Apple TV.
Fans of the hit sitcom will know that Sheldon (Jim Parsons) had a first roommate, Sebastian (Oscar nominee Steven Yeun), prior to Leonard (Johnny Galecki) moving in.
You probably don't expect to sue your roommate someday. Yet, it does happen. An agreement creates expectations to keep the living arrangement fair. They also provide protection and peace of mind because they are legally binding.
Sheldon and Leonard live together out of convenience not for financial reasons. Sheldon has said in the past that he wouldn't have a roommate if he could afford the rent. Penny on the other hand who lives alone on a smaller wage, is seen always struggling to get by, living paycheck to paycheck.
It was the one titled The Staircase Implementation. He moved in with Sheldon in 2003.