Formerly considered to serve only as structural components, sphingolipids are emerging as an important group of signaling molecules involved in many cellular events, including cell growth, senescence, meiotic maturation, and cell death. They are also implicated in functions such as inflammation and the responses to heat shock and genotoxic stress. Defects in the metabolism of sphingolipids are related to various genetic disorders, and sphingolipids have the potential to serve as therapeutic agents for human diseases such as colon cancer and viral or bacterial infections. The best-studied member of this family, ceramide, which also serves as the structural backbone for other sphingolipids, is an important mediator in multiple cellular signaling pathways. The metabolism and functions of sphingolipids are discussed in this review, with a focus on ceramide regulation in various cellular responses.