The mammalian target of rapamycin (mTOR), the target of the immunosuppressive drug rapamycin, is the central component of a nutrient- and hormone-sensitive signaling pathway that regulates cell growth and proliferation. This pathway becomes deregulated in many human cancers and plays an important role in the control of metabolism and aging. Sabatini’s lab has identified two distinct mTOR-containing proteins complexes, one of which regulates growth through S6K and another that regulates cell survival through Akt. These complexes, mTORC1 and mTORC2, define both rapamycin-sensitive and insensitive branches of the mTOR pathway. New results on the regulation and functions of the mTORC1 and mTORC2 pathways will be discussed.