Atrophic nonunions are the most challenging cases to treat among all nonunion situations, generally requiring multiple operations and long periods of recovery. It is of paramount importance for an orthopedic surgeon treating an atrophic nonunion case that he/she is in fact dealing with a clinical status in which vascularization of bone is very poor and cellular healing mechanisms are quite weak or absent. One of the most important steps of treatment in such cases is the grafting of the atrophic nonunion site, which is necessary for achieving biological stimulation. Preferring a graft that has a potent biological feature, rapid cellular cycle and a superior osteogenic capacity affects the nonunion treatment positively. For these reasons autogenous grafts are accepted as gold standard among all graft options. Donor site morbiditiy, limited availability and individual differences in the healing potentials of autogenous bone grafts have led to the search for synthetic biologic grafts as potential methods to enhance fracture healing. The osteoconductive and osteoinductive properties of allogeneic grafts, synthetic grafts, bioceramics, and heterogeneous grafts which are all products of biomedical researches are different from each other, and these unique biological properties are the most important criteria that determine the need and the type of the non-autogenous grafts to use in an atrophic nonunion case. Bone grafts and their biologic features, which we believe are the basis for a successful outcome in atrophic nonunion treatment, are summarized in this review.