The mammalian target of rapamycin (mTOR) is a multifunctional kinase that promotes cell growth and division in response to growth factor and nutrient signals. Rapamycin exerts its potent immunosuppressive effects in part through direct effects on antigen-specific lymphocytes; however, rapamycin also modulates adaptive immunity through its effects on innate immune cells, including dendritic cells and macrophages. Studies have established rapamycin-sensitive functions of mTOR, downstream of Toll-like receptors, in shaping the cytokine response of myeloid cells and driving the production of interferon by plasmacytoid dendritic cells. These findings point to new strategies for boosting or suppressing specific immune responses.