Nonunions of the femoral shaft represent a treatment challenge for the orthopaedic surgeon and a serious socioeconomic problem for the patient. Inadequate fracture stability, insufficient blood supply, bone loss or presence of infection are the main reasons for the development of a nonunion. Careful classification and exclusion of infection are crucial for the choice of the proper treatment alternative. Nail dynamization, primary intramedullary nailing or nail exchange, plate osteosynthesis and external fixation along with bone grafting, usage of bone substitutes and electrical stimulation can stimulate osseous union. A review of the aetiology, classification and treatment should prove helpful managing this serious complication.