In orthopedic oncology, massive bone allografts can be used as biological reconstruction of intercalary or articular defects after tumor resections. The main advantages of allografts are bone stock restoration and tendinous insertion, but the main drawback is the risk of mechanical complications, such as fracture, nonunion, and articular surface degeneration. Allograft-prosthesis composites reconstructions merge the advantages of allograft and prosthesis, preserving bone stock, providing a biologic tendinous insertion and a mechanical protection of the allograft. In intercalary reconstruction, the allograft can be used alone or in association with an autologous vascularized fibula, with the aim to achieve an early union and to improve the internal repair of the allograft, eventually obtaining a life-long lasting reconstruction. Hemicortical defect can be effectively reconstructed with appropriately shaped bone allograft segments, and custom-made cutting guides allow for precise multiplanar joint-sparing resection and hemicortical allograft matching. In the present chapter, authors illustrate tip and tricks in allograft reconstruction with the following techniques: allograft-prosthesis composite reconstruction of the proximal femur and proximal tibia in both adult and pediatric patients; allograft + vascularized fibula in intercalary reconstructions; patient-specific cutting guides in multiplanar joint-sparing resection and hemicortical allograft reconstruction.