From its Greek roots, ankylosing spondylitis (AS) means "stiff vertebra". AS is characterized by inflammation at the entheses, sites of attachment of ligaments, tendons, and joint capsules. The most commonly affected site is the sacroiliac joint. Cellular infiltration occurs without clear etiology and leads to erosion of bone. Subsequently, ossification of extraspinal joint capsules occur and vertebra fuse causing the characteristic "bamboo spine" radiographic appearance. Additionally, thoracic pathology leads to chest pain and reduced chest wall expansion. Extra-articular manifestations are common including uveitis.