The Bispectral Index (BIS) is a newly processed electroencephalogram parameter that was specifically developed to measure the hypnotic effects of anesthesia. Results from volunteer studies demonstrate that BIS correlates well with clinical assessments of sedation induced by sedative-hypnotic drugs. Clinical utility studies have shown also that BIS monitoring allows for better titration of anesthesia, resulting in lower hypnotic drug use and improved recovery. The data suggest that improved anesthetic titration with BIS provides sufficient clinical and economic benefits to justify its routine use. This article summarizes the clinical development and validation of BIS and describes how BIS monitoring can be used to improve anesthetic outcomes.