Jonathan Sprent has been at the forefront of research in T cell immunobiology for 30 Years. In early studies he defined the lifespan and migratory properties of recirculating T and B cells and showed that T cell exposure to antigen in vivo causes MHC-restricted trapping followed by proliferation and entry of effector cells into the circulation. He clarified the mechanisms of MHC-restricted T-B collaboration and, with others, developed the concept that T cell differentiation in the thymus involves a combination of positive and negative selection. He has also made important contributions in the fields of transplantation immunity, immunological tolerance and memory.