This Funding Opportunity Announcement (FOA), issued by the National Institute on Aging (NIA) at the National Institutes of Health, solicits grant applications that propose extension of research activities on osteoimmunology in order to broaden our understanding of aging aspects of osteoimmunology, using animal models. Most studies in this field have been conducted in young mouse models (usually animals less than 6 months of age). Under those conditions, it is not possible to ascertain the effects of aging in the balance between bone metabolism and immune function. Studies sought under this FOA should focus on the impact of the age-related decline in immune function on bone homeostasis or conversely on the age-related changes in the bone marrow niche affecting the immune interactions with bone. Research in osteoimmunology aims to understand the interplay between the immune and skeletal systems, and how these interactions lead to disease when disrupted. In the clinical setting, such disequilibria and the resulting diseases are most commonly found in the elderly, which are afflicted by both immune senescence and loss of bone homeostasis. This FOA is intended as a vehicle to allow investigators already working in the field of osteoimmunology to expand the scope of their research, so as to allow an enhanced understanding of the field within the context of the clinically relevant setting of aging.