The medial and posteromedial regions of the knee are important for knee stability but also frequently injured. Medial ligaments and capsule are primary and secondary stabilizers of valgus, rotation, and anterior and posterior translation. In the setting of rupture of the cruciate ligaments, it is important to identify injuries in this region because it can possibly alter the treatment strategy and even delay or prevent successful reconstruction of the cruciate ligaments. Injuries may occur to the superficial and deep medial collateral ligament, the posterior oblique ligament, the posteromedial capsule, and the semimembranosus tendon and its attachments. Meniscocapsular separation is associated with these injuries, and if normal movement of the meniscus and tension of the capsule and ligaments is altered, instability and eventually osteoarthritis may occur. Injuries to the posteromedial corner may be underdiagnosed. This article reviews the anatomy and imaging findings in the medial and posteromedial regions of the knee.