Ankylosing Spondylitis is a disease characterized by sacroiliitis and inflammation of the spine and tendon attachments. It commonly causes dull low back pain, bony tenderness, and arthritis. Over time, it can lead to a loss of spinal mobility and changes in posture like loss of lumbar lordosis and accentuated thoracic kyphosis. Disease progression is measured by factors like loss of height, limited chest expansion, and spinal flexion. Poor prognostic markers include early onset disease, early hip involvement, and smoking. Common extraarticular manifestations include anterior uveitis, inflammatory bowel disease, and psoriasis. Disease activity is measured by tools like the BASDAI and BASFI scales.