Dysfunction of the posterior tibial tendon is increasingly recognized as an etiology leading to acquired flatfoot in adults. Increased awareness of this condition during the past fifteen years has resulted in intensive study of the basic science and pathophysiology behind this clinical syndrome. New regimens for clinical assessment and treatment have been developed. Although much progress has been made in the recognition and treatment of this condition, many controversies and unanswered questions remain. This article will review the current thinking with regard to the pathophysiology, clinical evaluation, and decision-making process for the treatment of this common, debilitating condition.