Anxiety, anger, depression, and curiosity are major indicators of psychological distress and well-being that require careful assessment. Measuring these psychological vital signs is of critical importance in diagnosis, and can facilitate treatment by directly linking intense emotions to the events that give rise to them. The historical background regarding theory and research on anxiety, anger, depression, and curiosity is briefly reviewed, and the nature and assessment of these emotional states and personality traits are examined. The construction and development of the State-Trait Anxiety Inventory (STAI), the State-Trait Anger EXpression Inventory (STAXI-2), and the State-Trait Personality Inventory (STPI) to assess anxiety, anger, depression, and curiosity, and the major components of these emotional states and personality traits, are described in detail. Findings demonstrating the diverse utility and efficacy of these measures are also reported, along with guidelines for their interpretation and utilisation in research and clinical practice. Research with the STAI, STAXI and STPI over the last 40 years has contributed to understanding vitally important measurement concepts that are especially applicable to the assessment of emotions. These concepts included the state–trait distinction, item intensity specificity, and the importance of items that describe the presence or absence of emotions.