The Fundamentals of Spine Surgery first aims to investigate the efficacy of several therapeutic modalities in the modern treatment of spinal pathologies. Following this, the authors aim to estimate fusion by 3D CT scan in XLIFs applied in adult lumbar deformities, evaluating the clinical results related to fusion. The safety and effectiveness of minimally invasive-transforaminal lumbar interbody fusion in the treatment of lumbar degenerative spondylolisthesis is evaluated, highlighting the steps and technical procedures of this operation as well as its short and long-term outcomes. In the closing study, the authors compare the effectiveness of spino-pelvic parameters in minimally invasive posterior lumbar interbody fusion and traditional posterior open approach in the treatment of a prospective randomized series of high-grade adult isthmic spondylolisthesis.