Failed anterior cruciate ligament (ACL) reconstruction presents a difficult clinical challenge. Successful revision ACL reconstruction depends on identifying the causes of failure and correcting technical or diagnostic errors. Failed ACL reconstruction may be either traumatic or atraumatic. Atraumatic failures may be attributable to technical errors, diagnostic errors, or failure of graft incorporation. Published outcomes of revision ACL reconstruction have been worse than for primary ACL reconstruction. The preoperative evaluation, surgical techniques, and clinical outcomes of revision ACL reconstruction are reviewed.