Many cells in the human body are quiescent—that is, they are not actively dividing to create new cells, but can reenter the cell division cycle and proliferate at some later time. Among the cells that can survive in a quiescent state are lymphocytes that can become activated to mount an immune response, and dermal fibroblasts that can be called upon to aid in wound healing. The ability to enter and exit quiescence appropriately, and to remain viable while quiescent, is central to tissue homeostasis and the response to potentially life-threatening challenges. Yet, despite the central role of quiescence in normal physiology and pathophysiology, fundamental questions about quiescence remain unanswered but are currently being addressed.