Jason G. Cyster is an Australian-born American immunologist known for his work on lymphocyte migration, cell interaction dynamics in immunity, and the role of lipid mediators such as sphingosine-1-phosphate (S1P) in immune cell trafficking. He is currently a professor in the Department of Microbiology and Immunology at the University of California, San Francisco (UCSF) and an investigator with the Howard Hughes Medical Institute.