Research on emotion regulation (ER) strategies has often relied on trait self-report measures, where individuals retrospectively report their tendency to engage in a specific strategy. Although this method is convenient and useful in many clinical and research settings, it is subject to a number of response and memory biases and may not accurately reflect ER as it is naturalistically employed in daily life. We examined the ecological validity of 10 self-report measures of ER strategies (i.e., acceptance, behavioral avoidance, experiential avoidance, expressive suppression, procrastination, reappraisal, reflection, rumination, savoring, social support) with their reported daily use in intensive longitudinal designs in two samples (109 students, 135 treatment-seeking adults). Zero-order correlations revealed convergence between most trait measures and their daily ER strategy counterparts. However, analyses evaluating the specificity of trait measures in their associations with daily ER strategies (both zero-order and multivariate) did not support trait measures' discriminant validity. Rather, correlations between trait measures and factors of the between-person variance in daily ER strategies suggest that most ER trait measures may reflect broader tendencies to use or not use avoidance strategies in daily life. Implications for research using trait measures of ER strategies and recommendations for ER strategy assessment are discussed.