Stifle injuries are increasingly recognised as a major cause of hind limb lameness and commonly affect the soft tissues of the joint in adult horses, making ultrasonography a vital part of diagnostic imaging of this joint. This article aims to provide an introduction to stifle ultrasonography. To ensure comprehensive evaluation of the stifle, a systematic approach is necessary. The ultrasonographic examination is divided into five approaches: initially weight-bearing scans should be obtained of the cranial aspect (for the femoropatellar joint), medial aspect (for the medial femorotibial joint), and lateral aspect (for the lateral femorotibial joint), followed by flexed views from cranial (for the cranial aspect of the femorotibial joints) and, finally, in limited cases because pathology is rarer and the technique more demanding, weight-bearing views of the caudal aspect (for the caudal parts of both femorotibial joints). For the femoropatellar joint, ultrasound can be used to identify bruising (haematoma), injuries to the patellar ligaments, trochlear ridges (including osteochondrosis), and patella and tibial crest fractures. For the femorotibial joints, injuries to the menisci are the most common, but ultrasound can also identify rarer collateral and cruciate ligament injuries. and abnormalities of the weight-bearing surfaces of the femoral condyles, such as cartilage damage and subchondral bone cysts.