Mechanical low back pain (LBP) is an injury or derangement of an anatomic structure in the low back. When evaluating patients with LBP, clinicians should maintain clinical suspicion for vertebral fracture, cancer, and cauda equina syndrome. Management includes patient education focused on exercise, massage, and behavioral approaches such as cognitive behavioral therapy. Acupuncture can be an effective alternative and specific herbal supplements may provide short-term pain relief. The prognosis for patients with mechanical LBP is good. Inflammatory LBP is pain resulting from a systemic inflammatory condition, often referred to as axial spondyloarthritis. Ankylosing spondylitis is chronic inflammatory LBP characterized by early onset (mean age 24 years), with a higher prevalence in men. Five clinical parameters can help identify inflammatory LBP: improvement with exercise, pain at night, insidious onset, onset at younger than 40 years, and no improvement with rest. Management of inflammatory LBP typically includes nonsteroidal anti-inflammatory drugs and structured exercise programs, with emphasis on the involvement of a rheumatology subspecialist. Spondyloarthritis is associated with other rheumatic or autoimmune conditions, including rheumatoid arthritis, inflammatory bowel disease, and psoriasis. These should be considered when evaluating patients with inflammatory LBP.