Patients with advanced breast or prostate cancers usually develop bone metastases. The principal complications resulting from metastatic bone disease are pain, spinal cord compression, pathologic fractures and bone marrow suppression. Improving the management of bone metastases is crucial to quality of life for patients with breast and prostate cancer. Advances in understanding of the molecular mechanisms underlying the pathophysiology of bone metastasis are driving the development of new therapeutic strategies. The book provides an overview of molecular factors that offer targets and avenues for therapeutic strategies.