The pact was made on June 30, 2004 between Leonard and Howard. The pact was that when one of the two guys got a girlfriend, that girlfriend would set up he single guy with a female friend of hers.
The pact first appeared in "The Creepy Candy Coating Corollary" where Leonard and Penny were dating and Leonard told Penny about the Girlfriend Pact and although she felt reluctant about the pact, she eventually agreed to it. Later, Leonard and Penny were out with Howard in Leonard's car and Penny had chosen to set Howard up with Bernadette Rostenkowski, a girl working with her at the Cheesecake Factory as a waitress to put herself through grad school, where she was studying microbiology. During the date, Howard and Bernadette weren't getting along too well until they found out that they both have overbearing mothers where they then felt a connection after Howard's mother called him and Howard didn't pick it up and then the two of them started talking about their mother issues.
The pact appeared again in "The Desperation Emanation" where this time the setting up was the other way around: Howard's girlfriend, Bernadette set Leonard up with a female friend of hers. Bernadette's friend was a crass, unladylike, loud and obnoxious girl called Joy who attended Israeli Krav Maga with Bernadette. While she was crass and unladylike, she then hinted that accompanying her to a wedding would result in sex, Leonard jumped at the opportunity.