Knowledgeable treatment of diseases, deformities, and injuries of the musculoskeletal system requires an understanding of the complex, constantly changing nature of bone. Current orthopaedic practice relies on the ability of surgeons to drill, cut, ream, and realign bone; to fix one piece to another with screws, plates, wires, or rods; and to obtain union between bone and plastic or metal implants. The success of many of these procedures is often attributed to the technical skill of the surgeon or to the design of an implant or instrument, but it is actually the remarkable properties of bone that these properties can compromise the most technically expert orthopaedic treatment, whereas understanding them well can help to solve the most complicated clinical problems.