Knee replacement surgery is the most common joint replacement surgery in England and Wales. Postoperative radiographs are associated with long-term outcome at both early and late stages, and their correct interpretation is therefore vital. These radiographs will commonly be assessed by surgical trainees, emergency doctors, orthopaedic surgeons, nurse practitioners, and radiologists. The aim of this paper is to provide the reader with a systematic approach to assessing these radiographs, whether it be in the immediate postoperative period or during subsequent follow-ups, and to provide sufficient knowledge to critique the procedure. An outline of prostheses and their indications alongside a comprehensive review of the assessment of important angles, alignment, and correct positioning of femoral and tibial components is presented.