Autonomic nervous system's role as a "life-sustaining" system is well known. However, the anatomical and functional complexity of ANS, makes difficult its monitoring in perioperative setting. Various methods have been proposed for measuring its activity. The current review focuses on selected tools-electrodermal activity, pupilometry, heart rate variability, surgical skin index and salivary-a amylase-and their application in the field of anesthesia, intensive care and emergency medicine.