A better understanding of the biology of fracture healing and an increasing awareness of the limitations and potential complications of autogenous bone graft harvest have combined to foster a burgeoning interest in the development of bone graft substitutes. A few of these materials have been available for more than a decade, and many more should become available in the near future. The characteristics of the ideal bone graft substitute may vary considerably depending on the intended site of application and the clinical setting in which it is used. Knowledge of the available alternatives is a necessary prerequisite to informed decision making.