Enthesitis is the inflammatory process marked by the insertion of tendons, ligaments and joint capsules on the bone and it is a cardinal feature (and diagnostic criteria) of spondyloarthropathies (SpA). Although it is usually revealed by clinical examination, recent studies using magnetic resonance imaging (MRI) and ultrasonography (US) have confirmed that enthesitis (as well as synovitis) can often be asymptomatic, both in the axial and peripheral skeleta. Therefore, a systematic US study of peripheral entheses could be useful in the diagnostic process of patients suspected with SpA, and peripheral enthesitis scoring systems have been proposed. Recently, power Doppler US (PDUS) has been proved to be useful for differentiating mechanical and inflammatory enthesitis and for monitoring the efficacy of therapy. This article reviews the main anatomical and histopathological aspects of enthesitis and describes the general US features of enthesis and the basic US features of enthesitis, in its various stages. The usefulness of US and PDUS in the diagnosis and assessment of SpA is discussed on the basis of the available literature and our experience.