Jim meets Dunder Mifflin salesperson Karen when he transfers to the Stamford branch. Karen later develops a crush on Jim. The two begin a formal relationship after Stamford and Scranton merge, but Jim's feelings for Pam make it difficult for the romance to progress.
In "The Job", Jim, Karen, and Michael all interview for the corporate position, and during his interview Jim finds a sweet note from Pam in his briefcase. After the interview, he drives straight back to Scranton to pursue Pam, leaving Karen alone without a ride. Jim asks Pam to dinner, and they begin a relationship that ultimately leads them to the altar. In the "Office Summer Vacation," Karen says that Jim "dumped her ass" and left her crying at a fountain in New York.
When Karen appears later in the Season 5 episode "Lecture Circuit," it is revealed that she is 8 months pregnant and happily married to a dermatologist named Dan.
Status: Broken up, but presumably friends