Originally shown to promote the growth and activation of B cells, thymic stromal lymphopoietin (TSLP) is now known to have wide-ranging effects on both hematopoietic and nonhematopoietic cell lineages. These include dendritic cells, basophils, mast cells, B cells, epithelial cells, and CD4+, CD8+, and NK T cells. Although TSLP’s role in the promotion of Th2 responses has been studied extensively in the context of lung-and skin-specific allergic disorders, it is becoming increasingly clear that TSLP may impact multiple disease states within multiple organ systems. This review highlights recent advances in the understanding of the surprising role of TSLP in the control of a variety of cancers, both solid tumors and leukemia, in which the TSLP/TSLP receptor axis was shown to be an important regulator.