Acromioclavicular (AC) joint injuries, which are very common in the athletic population, with both acute and chronic presentation, cause separation of the internal joint components. The anatomy and inherent three-dimensional configuration of the AC joint make it a resilient joint that can resist a significant amount of force before separation or disruption. A detailed knowledge of AC joint is of pivotal importance for the orthopedic surgeons during both arthroscopic and open shoulder surgery. None of the more than 150 different surgical techniques can claim to be a gold standard to address the injury and there is still discussion about indications for conservative or surgical treatment. In this chapter, the anatomy and biomechanics of the AC joint, as well as the assessment, diagnosis, and different treatment strategies including our preferred protocols for various types of injuries, are reviewed.