Abstract: Appropriate pain management in critically ill patients greatly depends on a clinician’s ability to perform reliable and valid pain assessment. Subjective pain assessment tools are available to clinicians when patients are able to complete selfreport tools, the “gold standard” of pain assessment; however, objective pain assessment tools may be appropriate when patients are not capable of adequate communication because of sedation or mechanical ventilation. The pain assessment tools for critically ill patients were elaborated in this article to provide reference for improving the process of pain assessment and management.