Radiation and bisphosphonate induced mandible osteonecrosis have distinct underlying physiopathological mechanisms, but both can constitute a serious problem and lead to functional impairment and facial disfigurement. The aims of treatment are the elimination of pain and associated infections, improvement of mouth function (opening, speech, mastication), and the prevention of deformity (fistulas, bone exposures, bone defects, pathological fractures). For patients with advanced refractory disease, pathological fracture, oro-cutaneous fistula and severe osteolysis, ressection associated with microvascular reconstruction seems to be a valid option that stops the underlying pathophysiology of overinfected avascular bone necrosis. In this book, we describe different clinical situations related to several grades of osteonecrosis, where different options of free transfer should be considered based on case-specific phypathosiological mechanisms. We propose a simple clinical grading system to predict the best treatment option.