Notch signaling plays a preeminent role during development in not only regulating cell fate decisions, but it can also influence growth and survival of progenitor cells. In the immune system, Notch is required for the maintenance of hematopoietic stem cells and in directing T- versus B-lineage commitment. In this review, I will summarize some of the recent findings relating to the function of Notch in the immune system during lymphocyte development and in the generation and function of mature cells.