Inorganic polyphosphates (PolyP) are linear polymers containing a few to several hundred orthophosphate residues linked by energy-rich phosphoanhydride bonds. PolyPs are widely used as reagents in water treatment, fertilizers, flame retardants and food additives due to its unique properties, inexpensiveness, nontoxicity and biodegradability. The practice of enhanced biological phosphorus removal (EBPR), based on PolyP accumulation by sludge bacteria, is an accepted and low-cost strategy for controlling eutrophication. PolyPs are present in the cells of all living organisms, from bacteria to mammals. They perform numerous functions in the cells: phosphate and energy storage, sequestration and storage of cations, formation of membrane channels, cell envelope formation and function, gene activity control, regulation of enzyme activities, stress response and stationary phase adaptation. PolyPs participate in bone tissue development and in the blood coagulation cascade and are promising candidates in therapy for bone and blood diseases. They may also have application in creating novel bone substitute materials, serving as carriers for prolonged action drugs, and acting as a phosphodonor in enzymatic synthesis of biologically active compounds. The importance of polyphosphate kinases in the virulence of pathogens forms a basis for the development of new antibiotics. Further study of PolyP biochemistry and cell biology can be applied to medicine, environmental protection and agriculture. (C) 2011 Elsevier Ltd. All rights reserved.