A basic science and clinical review of low back pain due to the lumbar zygapophysial (facet) joints was performed based on a literature search of scientific journals and textbooks. Recent studies estimate that 15% to 40% of chronic low back pain is due to the zygapophysial joints. The histological basis for zygapophysial joint pain has been scientifically established, but the precise clinical etiology remains undetermined. There are no unique identifying features in the history, physical examination, and radiological imaging of patients with pain of lumbar zygapophysial joint origin. Spine physicians diagnose zygapophysial joint pain based on analgesic response to anesthetic injections into the zygapophysial joints or at their nerve supply. Studies on treatment of isolated zygapophysial joint pain are limited. This review summarizes current understanding of lumbar zygapophysial joint disorders while highlighting the need for additional research.