the character
Karen Filippelli was introduced in the third season premiere of The Office (US) ("Gay Witch Hunt") as an employee of Dunder Mifflin's Stamford, Connecticut branch, where Jim transferred at the end of season 2. When the Stamford branch closes, she considers moving to Scranton while Jim encourages her to move to New York. This disappoints her, as she formed a crush on Jim. Later, Jim tells her that he's going back to Scranton and that she should as well. Karen and several other employees (including Andy Bernard and Jim) transfer to the Scranton branch, though after Christmas, most of the original Stamford employees quit.
She becames romantically involved with Jim for several months, but sometimes has trouble fitting in with other Scranton coworkers. In the third season finale "The Job," both Jim and Karen interview in New York for a corporate position at Dunder Mifflin, however former temp Ryan Howard gets the job over both of them (and Michael Scott, who also interviewed but found out that he would be taking girlfriend Jan Levinson's job). Through previews for season four and in the premiere "Fun Run," we find out that Jim broke up with her and (in her words,) "left my ass crying by a fountain in New York." Also in Fun Run, Jim reveals that Karen told him she wasn't leaving just because they broke up, but found her desk empty the next morning.