The Depression Anxiety Stress Scales (DASS) is a tool used by psychologists to measure negative emotions like depression, anxiety, and stress. It provides individual scores for each emotion and an overall score for general mental health. The DASS is used worldwide in both general and clinical populations. In this chapter, the background of depression, anxiety, and stress is discussed along with the history of the scale’s development and validation. The DASS has been shown to be a reliable and valid measure of these negative emotions. This tool has been translated into several languages and has been tested across different cultures. The importance of measuring negative emotions is significant because it helps clinicians identify and treat mental health problems. The DASS is a useful tool for screening, diagnosing, and monitoring treatment progress for those experiencing such negative emotions.