Total hip arthroplasty (THA) is often used as a surgical option to salvage a previous hip surgery that has failed. This type of surgery offers significant challenges and requires additional surgical planning regarding previous hardware, considerations of surgical approach, and the possibility of anatomic deformity. THA in the setting of a previous hip surgery is deemed conversion hip arthroplasty. Various etiologies may include: Conversion hip arthroplasties carry their own unique set of challenges and may have different clinical outcomes than standard hip arthroplasty. This chapter will cover conversion hip arthroplasty following past surgery to the hip joint, proximal femur or acetabulum, including technical challenges, unique considerations, and clinical outcomes.