Bone serves not only as a locomotive organ but also as an organ instrumental in many other functions such as hematopoiesis. To this end, bone undergoes renewal by sequential resorption and formation. Bone resorption and formation are regulated by many systems including the endocrine, the nervous and the immune systems. The skeletal and the immune systems are closely related because they share many regulatory molecules such as cytokines and transcription factors. Studies on such shared molecules and inflammatory bone destruction in rheumatoid arthritis have fostered a novel interdisciplinary field, "osteoimmunology". Advances in osteoimmunology may lead to the novel therapeutic strategies in bone and immune diseases.