Heterotopic ossification (HO), the development of bone outside its normal location in the skeleton, can compromise outcomes of total hip arthroplasty (THA). The etiopathogenesis of HO, though incompletely understood, involves genetic abnormalities, neurologic injury, and musculoskeletal trauma. Several systems are used to classify severity of HO after THA. Numerous risk factors for HO, including patient factors and surgical techniques, have been described. Prophylaxis against HO traditionally has involved radiation therapy or use of nonsteroidal anti-inflammatory drugs. Once formed, heterotopic bone can be managed only with surgical excision.