Instability is a common failure mode following both primary and revision total hip arthroplasty (THA). Advancements in the understanding of the mechanisms of failure and prevention of postoperative instability have provided a framework to address this complication. This chapter reviews the incidence of, patient factors relating to, and surgical factors impacting postoperative instability. It further identifies the state of the art in the management of instability and outlines the author’s preferred treatment strategies.