Delayed union represents an ongoing failure of initial fracture management. It still occurs partly because the precise reason why a patient's fracture does not heal frequently is unknown. This article aims to outline the limited material available on the pathophysiology of delayed healing. The systemic status of the patient, local limb status before injury, the nature of the traumatic injury, local host response to the injury, potential negative impact of orthopaedic fracture care, and pharmacologic variables are considered.