This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation which form a major part of the ICRP system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell "niches," radiosensitivity to acute and protracted exposures, is presented in a series of substantial reviews as Annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin and bone. This foundation of...