The aim of this review is to detail the pathophysiologic mechanisms occurring during bone metastases. osteolytic and osteosclerotic metastases are observed after migration of malignant cells coming from a primitive tumour which can localize and grow inside the hematopoietic bone marrow. Bone lesions observed during hematologic malignancies (lymphomas and myeloma) are not detailed here. The various cytokine networks that are occurring in bone metastases are detailed: in both cases there is a "vicious circle" between the the tumoral cells and bone cells responsible for the physiological remodeling of bone. The knowledge of these interferences permits to understand the use of anti-osteoclastic treatments (bisphosphonates) in osteolytic as well as osteosclerotic metastases.