Lumbar interbody fusion is an established surgical technique for a variety of conditions affecting the lumbar spine. A large number of interbody fusion devices made of differing materials are now available for use. Approaches for interbody fusion include anterior lumbar interbody fusion, oblique lumbar interbody fusion, lateral lumbar interbody fusion, axial lumbar interbody fusion, transforaminal lumbar interbody fusion, and posterior lumbar interbody fusion. This chapter discusses the biomechanics of lumbar interbody fusion devices and approaches and the clinical rationale and the clinical results of each approach. The advantages and disadvantages of each approach are compared and contrasted. The importance of an appropriate preoperative assessment to determine the best approach for interbody fusion is emphasized, taking into account the condition being treated, sagittal balance, bone quality, and contraindications to a specific approach. The best approach to lumbar interbody fusion by indication and surgical level(s) is discussed.