This review covers not only the current status of the field but also the evidence on which the concept of ATP compartmentation is based. It is hoped that such a survey may help to stimulate work in this area and to broaden the appreciation of its reality and functions. Some may be surprised to learn that mature human erythrocytes, known to be devoid of intracellular organelles, can sequester ATP, but they may not have taken into account the possible roles of the complex cytoskeleton that is tethered to the cells' plasma membrane. The functional significance of the ATP pools springs from the likelihood that they serve as both an energy reserve, capable of sustaining ion pumping during periods of transient stress, as well as a putative transduction mechanism by which the cell's cytoskeleton may sense cellular energy stores.