Centuries ago, during the industrial revolution, rickets, also called 'the English disease', spread rapidly among city-dwelling poor children and became endemic due to vitamin D deficiency and insufficient access to sunlight. Nowadays it appears to be endemic again as the increase of vitamin D deficiency is paralleling the primacy of breast-feeding in Western societies. Breastfeeding, nutritional status and dark skin are the main risk factors for rickets or 'rachitis' as is the correct medical term. Rickets is a childhood disorder and the basis for understanding the disease is rooted in the concept of mineral metabolism and its control mechanisms in the growing fetus, infant and child. As it is now understood that rickets is not only caused by vitamin D deficiency, it has to be kept in mind that vitamin D and calcium deficiency is prevalent in developing countries as well as in affluent societies, where children and their mothers are not exposed to as much sunlight as they need. The rapid growth in molecular biology has been exemplified in the application of subcellular technologies to study vitamin D in human and animal models. In this volume the latest research on vitamin D and rickets is presented from different perspectives such as the interesting historical overview to bone metabolism, molecular genetics of vitamin D and conclusions for disease prevention. It will be of special interest to pediatricians, endocrinologists and health care specialists who work with children at risk for the disease.