Adult spinal deformity (ASD) is a complex disease state that pathologically alters standing upright posture and is associated with substantial pain and disability. This article provides an overview of classification systems for spinal deformity, clarifies the need to differentiate between pediatric and adult classifications, and provides an explanation on the use of the Scoliosis Research Society-Schwab Adult Spinal Deformity Classification (SRS-Schwab ASD Classification). This information allows surgeons, researchers, and health care providers to (1) identify sources of pain and disability in patients with ASD and (2) accurately use the SRSeSchwab ASD Classification to evaluate patients with ASD.