Many types of adult stem cells exist in a state of cell-cycle quiescence, yet it has remained unclear whether quiescence plays a role in maintaining the stem cell fate. Here we establish the adult germline of C. elegans as model for facultative stem cell quiescence. We find that mitotically dividing germ cells, including germline stem cells, become quiescent in the absence of food. This quiescence is characterized by a slowing of S phase, a block to M-phase entry, and the ability to re-enter M phase rapidly in response to re-feeding. We also demonstrate that cell-cycle quiescence can maintain the stem cell state. The signaling pathway required for stem cell maintenance under conditions of active proliferation (GLP-1/Notch signaling) becomes dispensable under conditions of quiescence. We find that quiescence stabilizes Notch effector proteins, suggesting that changes in protein stability may underlie the effect of quiescence on stem cell maintenance. We are currently investigating the food signals required for quiescence exit, as well as the role of cell-cycle regulators in maintaining quiescence.