It has only recently been appreciated that the immune and skeletal systems have major interactions. It is now well documented that osteoclasts, which are important cellular mediators of skeletal homeostasis, are derived from hematopoietic precursors that also give rise to immune cells. In addition, numerous cytokines that were first shown to regulate immune cell function have also been demonstrated to regulate bone cells and influence skeletal health. Conversely, products of bone cells appear critical for the engraftment of marrow in bone and the normal development of the hematopoietic and immune systems. In the past scientists involved in immune and bone cell investigations have rarely interacted in a significant way as these disciplines have developed independently and, for the most part, remain separate. To our knowledge, no previous scientific meeting has been convened to specifically bring together the members of both fields. The goal of the proposed meeting is to allow these scientists to interact so that new collaboration can develop and more rapid progress in understanding the relationships between the immune system and the skeletal system can be achieved. The fundamental hypothesis of the organizers is that progress in the field of osteoimmunology will be delayed unless better communication is established between bone biologists and immunologists. We believe that a primary way to enhance collaborations between scientists in these previously separate disciplines is to bring the members of both fields together at a conference in which all participants can interact freely and share ideas. The conference will be held on May 26, 2006 to June 2, 2006 in Crete, Greece. ? ? ? ?