There is no clear consensus on spinal fusion criteria for lumbar degenerative disease based on high quality evidence. The significances of the addition of fusion surgery to posterior decompression in surgical interventions for these diseases is the mechanical removal of a painful unstable interbody segment, assumed to be the cause of appearance and/or an exacerbating factor of low back pain and neurological symptoms, in addition to correction of the spinal deformity. In this article, we describe several unresolved issues, namely, pathological differentiation of low back pain, fusion surgery for discogenic low back pain, radiological definition of spinal instability, and the clinical impact of vertebral slippage and/or instability, which are considered grounds for selecting fusion surgery but remain controversial. Following the more recently the development and spread of minimally invasive posterior decompression techniques, it is now necessary to reevaluate the fusion criteria for degenerative spondylolisthesis as indicated in recent years by the dramatic increase in fusion surgery. We therefore discuss the indications for and problems of posterior decompression alone and fusion surgery for degenerative lumbar disease, focusing on degenerative spondylolisthesis, and furthermore give an overview of a lateral lumbar interbody fusion.