Lumbar spinal stenosis is often the result of advanced degeneration of motion segments of the lumbar spine. Loss of disc height, facet displacement and hypertrophy, spondylosis, and spondylolisthesis, as well as buckling of the ligamentum flavum and annulus fibrosus, all contribute to impingement on the spinal canal and intervertebral foramen in lumbar stenosis. There is a subgroup of patients with spinal stenosis in whom the spine is unstable preoperatively or becomes destabilized following decompression who would benefit from an initial fusion procedure. Posterior lumbar interbody fusion (PLIF) addresses several aspects of the multifactorial pathophysiology responsible for spinal stenosis and may arrest the degenerative changes at the fused level. Fusion, in particular PLIF, should be considered in complex cases of lumbar spinal stenosis, most notably in patients with postlaminectomy stenosis or stenosis associated with spondylolisthesis.