Autologous bone marrow serves as the richest and most readily available repository of progenitor cells capable of differentiating into mature bone forming cells. Numerous studies have demonstrated that bone marrow alone or cell suspensions of marrow usually diluted in culture medium affect de novo bone formation when implanted in soft tissue sites. Consequently, when bone marrow is used to enrich orthopaedic grafting matrices such as xenograft, demineralized bone matrix, or ceramic materials it almost invariably produces faster and more consistent defect healing compared to bone marrow or the carrier matrix alone and, in some cases, equivalent healing to autograft. This article evaluates the clinical effectiveness of these grafting materials for various orthopaedic applications such as healing long bone defects and enhancing spinal fusion procedures, and hypothesizes that enrichment with bone marrow is integral to timely and satisfactory graft incorporation. Methods such as centrifugation, culture expansion and selective cell retention that concentrate and deliver marrow-derived osteoprogenitor cells to the graft site as a means of mimicking more closely the consistent bone forming potential of autologous bone graft are also discussed.