Spinopelvic sagittal alignment has been shown to play an important role in pediatric and adult thoracolumbar spinal deformity. However, less is understood about the importance of sagittal alignment in the cervical spine and patients with adult cervical deformity. The purpose of this review article is to provide a comprehensive overview of contemporary principles pertaining to adult cervical deformity. Upper cervical parameters, regional cervical parameters, cervical shape classifications, and cervical deformity classifications will be reviewed based on the current literature.