Pursuit of the enzymes that make and degrade poly P has provided analytic reagents which confirm the ubiquity of poly P in microbes and animals and provide reliable means for measuring very low concentrations. Many distinctive functions appear likely for poly P, depending on its abundance, chain length, biologic source, and subcellular location. These include being an energy supply and ATP substitute, a reservoir for Pi, a chelator of metals, a buffer against alkali, a channel for DNA entry, a cell capsule and, of major interest, a regulator of responses to stresses and adjustments for survival in the stationary phase of culture growth and development. Whether microbe or human, we depend on adaptations in the stationary phase, which is really a dynamic phase of life. Much attention has been focused on the early and reproductive phases of organisms, which are rather brief intervals of rapid growth, but more concern needs to be given to the extensive period of maturity. Survival of microbial species depends on being able to manage in the stationary phase. In view of the universality and complexity of basic biochemical mechanisms, it would be surprising if some of the variety of poly P functions observed in microorganisms did not apply to aspects of human growth and development, such as aging and the aberrations of disease. Of theoretical interest regarding poly P is its antiquity in prebiotic evolution, which along with its high energy and phosphate content make it a plausible precursor to RNA, DNA, and proteins. Practical interest in poly P includes many industrial applications, among which is its use in the microbial depollution of P1 in marine environments.