This paper provides a detailed review of the clinical aspect and engineering view of how to measure, interpret, model, and control general anesthesia. The mechanisms of anesthesia in terms of unconsciousness, amnesia, analgesia, and akinesia in modern balanced anesthesia are reviewed. The assessment and interpretation of anesthesia according to clinical signs (i.e., lacrimation, sweating, papillary dilatation), physiological monitors (i.e., electromyography, electrocardiography, blood pressure, electroencephalography, oxyhemoglobin saturation), and evaluation indices (i.e., bispectral index scale, entropy, auditory evoked potentials, and surgical stress index) are reviewed in order to define the objectives of general anesthesia. Finally, the intelligent modeling and control of anesthesia are thoroughly reviewed. Modern general anesthesia is moving towards the monitoring, interpretation, modeling, and control of multi-inputs from quantitative and qualitative nonlinear physiological signals and multi-outputs for drug control of unconsciousness, amnesia, analgesia, and akinesia. A multistage hierarchical system should thus be developed for the modeling and control of general anesthesia in the future.