Expressive suppression (ES), an emotion regulation strategy used to inhibit emotional expressions, is a functional skill that is used throughout individuals’ daily lives to manage emotional and social experiences. The ES process requires effort, which is likely applied based on circumstance variations (e.g., type and intensity of emotions, social presence, and motivation), and can lead to success. However, current literature has been singularly focused on one aspect of ES, frequency of attempts, using two limited techniques, questionnaires or experimental instruction during lab visits, with results often linking high ES frequency to poor psychosocial functioning. This has led to significant gaps in our understanding of (1) how ES functions (i.e., how effortful and successful it is), (2) how ES is applied based on circumstance variations, and (3) naturalistic and daily ES use. The current dissertation used a novel trait-level measure of context-dependent ES frequency, effort, and success (Study 1), experience-sampling method to assess daily variations in emotional and social circumstances and ES use (Study 2), and extreme groups design to assess differences in emotional experience and ES function in response to an emotion-eliciting lab stressor for high and low habitual suppressors (Study 3). Study 1 results showed that ES frequency, effort, and success varied based on emotion type, and frequency varied based on social presence. Results from Study 2 showed that ES effort varied in the moment based on emotion type and intensity, social presence, and motivation. Additionally, on average, ES effort varied based on motivation, highlighting differences in the within- versus between-person processes of ES. Study 3 results showed that ES success in the moment depends on ES effort, which depends on emotion intensity, but these relationships, their averages across study tasks, and emotional expression, did not differ for high and low habitual suppressors. Discussions focus on momentary variations in the ES process, as well as minimal individual differences in this process, highlighting ES as a functional skill when it is applied contingently in circumstances. Implications of these results, including cross-cultural differences in ES and expanding ES theory and research to include other forms of expression control, are also discussed.