Dendritic cell (DC) vaccination has generated intense interest as a potential cancer therapy. However, the rate limiting step has been the generation of DCs. Flt-3 ligand (FL) is a growth factor that was first discovered by its ability to stimulate the proliferation of hematopoietic progenitor cells of both lymphoid and myeloid origin. The remarkable activity of FL to induce large numbers of dendritic cells both in vivo and in vitro soon captured the interest of numerous researchers. In this review, we examine the structure and function of the FL, its antitumor activity in animal models, and its potential as a novel cancer treatment.