The contribution of the sacroiliac (SI) joint to low back pain is becoming increasingly recognized. Several studies have demonstrated that in patients presenting with low back pain, up to 25% may have pain that implicates the SI joint. Additionally, patients who undergo spinal fusion may have an increased rate of SI joint degeneration, further contributing to complaints of low back and referred lower extremity pain. Recognition of the SI joint as a contributor to low back pain does involve a paradigm shift for the spine surgeon. The goal of this chapter is to: Establish an understanding of the anatomy and mechanics of SI joint function and pathology Discuss clinical history and relevant physical exam and imaging findings Review diagnostic criteria and nonsurgical management options Outline a treatment algorithm and provide effective Minimally Invasive (MIS) Surgical treatment options