The term “spondyloarthritis” encompasses a variety of conditions that manifest as inflammation of the synovial membranes and entheses. The synovial inflammation lacks specificity and shares many features with rheumatoid synovitis. The hallmark of spondyloarthritis is inflammation of the entheses, which manifests as a combination of hyperostosis, osteitis, and periostitis. The entheses include not only the sites where tendons, ligaments, and joint capsules attach to bone, but also other fibrous structures such as the amphiarthroses (pubic symphysis, manubriosternal symphysis, and discovertebral junctions) and the diarthro-amphiarthroses (sacroiliac area, chest wall joints, and tips of the fingers and toes). This vast entheseal territory is the target selectively involved in patients with spondyloarthropathy.