Imaging has always been an integral part of the assessment of SpA. This group of diseases involving the axial skeleton and peripheral joints is a particularly intriguing area for sonographers, because it requires the evaluation of both articular and extra-articular regions. Among extra-articular features enthesitis has recently emerged as an area of special interest for both basic science and clinical researchers as well as for those working in the field of musculoskeletal imaging. This review provides information about research in this area focusing on the current concept and definition of enthesitis by US.