Crossbreeding is an old technology; however, when used in today’s dairy systems, crossbreeding can produce profitable results for dairy producers. Interest in crossbreeding of dairy cattle has become a topic of great interest in the last ten years and has developed in response to concerns dairy producers have about fertility, calving difficulty, and stillbirths in today’s genetically improved Holstein cows. This chapter summarizes landmark crossbreeding research at the University of Illinois before going on to consider crossbreeding research in Canada, Australia, New Zealand, the United States, Ireland and Germany. The chapter includes a case study focussing on crossbreeding with Jersey cows conducted at the University of Minnesota. Finally, the chapter looks ahead to future trends in this area and suggests further reading on the subject.