The effects of rheumatoid arthritis on bone include structural joint damage (erosions) and osteoporosis. The latter may lead to increased risk for fractures, which are associated with increased morbidity and mortality. Osteoporosis in rheumatoid arthritis is characterized by a complexity of risk factors, including primary osteoporosis risk factors in addition to inflammation, immobilization, and use of corticosteroids. Quantitative assessment of periarticular and generalized bone loss in rheumatoid arthritis may be reliable indicators of future disease course and potential response variables in intervention studies. The osteoclast cell in rheumatoid arthritis plays a crucial role in the development of erosions and periarticular and generalized osteoporosis, suggested to be mediated through the osteoprotegerin/receptor activator of Nuclear Factor (NF)-kappabeta/receptor activator of NF-kappabeta ligand signaling system. Based on an improved understanding of this biology, new treatment opportunities exist.