Nutrition and Osteoporosis: Seeing Through a Glass, Darkly (1 Cor. 13:12) This volume of Advances in Nutritional Research deals with the present state of knowledge relative to the role of nutrition in the etiology of osteoporosis, one of the most serious degenerative diseases in the aging population. As a back­ drop for subsequent chapters on specific nutrients, Chapter 1 provides a com­ prehensive account of the gain and loss of bone throughout the life cycle, with emphasis on the architectural changes in later life that predispose to osteoporotic bone fractures. Chapter 2 documents the occurrence of aging bone loss through­ out human archeological history and Chapter 3 extends this documentation to all non-human vertebrate species so far examined, including primates living in the wild. It is apparent that a progressive loss of bone tissue is a normal accompaniment of aging among higher vertebrates. Whether it is a cause of bone fractures in animals, as it is in humans, is still unknown. It has also been established that there are significant differences in the frequency of osteoporotic fractures among human families, ethnic groups, national populations and diet cultures. Numerous studies have been carried out in an effort to explain these differences, and many of these deal with the possible effect of nutrition. Protracted controversies over the role of nutrition in the etiology of osteoporosis are reflected in the contents of several of the ensuing chapters.