Julie was Ross's girlfriend for the beginning of the second season. Julie and Ross knew each other when they were in grad school, and they were reunited during a dig in China. Julie entered the lives of the friends at a bad time, seeing as Rachel had found out about Ross's feelings for her just prior to learning about Julie. Thus, Rachel does not like Julie because Rachel feels like Julie has stolen Ross from her.
After Ross learns about Rachel's feelings for him, he dumps Julie as he pursues his love for Rachel again. His breakup with Julie did not go smoothly. Ross admits that he cried, she cried, she threw things and it hit him. Ross and Julie had a happy relationship for some time. Julie seems like a genuinely nice person and even has a talk with Rachel concerning how intimidated she (Julie) is by her (Rachel). Julie also forms a friendship with Monica, much to Rachel's disdain.
In The One With Russ, Julie appears during the credits scene where she hooks up with Ross's doppleganger,Russ.