Ultrasound is a therapeutic agent commonly used to treat sports-related musculoskeletal conditions, including tendon injuries or tendinopathy. Despite the widespread popularity of therapeutic ultrasound, few clinical studies have proved its efficacy. Several animal studies have been conducted to explore its effectiveness. In addition, a number of in vitro studies investigating the mechanisms underlying the ability of this physical modality to enhance tendon healing or to treat tendinopathy are in progress. There is strong supporting evidence from animal studies about the positive effects of ultrasound on tendon healing. In vitro studies have also demonstrated that ultrasound can stimulate cell migration, proliferation, and collagen synthesis of tendon cells that may benefit tendon healing. These positive effects of therapeutic ultrasound on tendon healing revealed by in vivo and in vitro studies help explain the physiologic responses to this physical modality and could serve as the foundation for clinical practice.