This chapter delves into the use of vascularized bone transfers for upper extremity bone defects. It highlights that while many bone issues can be resolved through simple fixation, larger defects, osteomyelitis, and tumor-related defects often require bone reconstruction. Vascularized bone transfers have traditionally been reserved for challenging cases, such as segmental defects longer than 5–6 cm, particularly in poorly vascularized areas like the lower extremities. The chapter emphasizes that bone defects smaller than 6 cm can often be successfully treated with nonvascularized grafts as long as they are covered with well-vascularized tissue and free from infection. Vascularized bone grafts are preferred for larger defects as they allow for primary bone healing, ensuring a stable microenvironment and not relying on recipient bone remodeling. Benefits of using bone flaps in upper extremity reconstruction are faster bone union, hypertrophy, and reduced late stress fractures compared to nonvascularized grafts. Bone flaps can be used effectively in challenging surgical conditions, including septic or irradiated areas. Indications for vascularized bone transfers in upper limb bone defects are discussed, emphasizing their suitability for cases where simpler techniques might fail, such as traumatic or oncologic large bone defects and nonunions due to infection, radiation, or previous surgeries. The chapter also explores the role of various donor sites and techniques, highlighting the advantages and considerations for each. It mentions the importance of selecting the appropriate donor site based on the size of the bone needed, distance from recipient vessels, and the need for soft tissue. Ultimately, vascularized bone grafts are valuable in treating upper extremity bone defects, offering advantages like improved blood flow and reduced infection risk. The choice of technique and donor site depends on the specific case, but vascularized fibular grafts are often preferred for large defects, while the medial femoral condyle flap is suitable for smaller vascularized bone needs. Vascularized bone grafts also allow for one-stage surgical reconstruction and resistance to infections due to autonomous vascularization.