Our knowledge of the significance of sarcopenia in old age is limited by a lack of epidemiologic data, an incomplete assessment of the pathophysiologic consequences of age-related decrements in muscle mass and quality, and poor understanding of the underlying mechanisms responsible for these decrements. These gaps prevent us from fully appreciating the extent of the public health burden that sarcopenia poses, and present major obstacles to the elucidation of therapies to prevent or reverse sarcopenia in the elderly. The National Institute on Aging convened the Workshop on Sarcopenia to address these issues. The primary questions explored at the workshop included: (a) What research is needed to determine the clinical and functional significance of sarcopenia? (b) What research is needed to understand its etiology? and (c) What opportunities are there for determining the efficacy of current or potential interventions to prevent or retard the development of sarcopenia? The research recommendations from the workshop underscored the need for more dialogue between researchers in different fields (e.g., endocrinology, exercise physiology, bone biology) and for multidisciplinary approaches in order to gain greater insight into sarcopenia. The summary of the research directions which follows has been organized according to the primary questions of the workshop.