["Journal of Personality, EarlyView. ", "\nABSTRACT\n\nIntroduction\nTheoretical work increasingly highlights emotion regulation flexibility (ERF), instead of ER frequency, as the core of ER effectiveness. Scarce research, however, has examined prospective relations between ERF and emotion intensity and dynamics.\n\n\nMethod\nAdopting a measurement burst design with month‐long daily diary assessments at two waves, this study investigated the prospective associations between different operationalizations of ERF (trait vs. state) and the intensity and dynamics (variability, instability, inertia) of positive and negative affect across 2.5 years (n = 175, 7985 total daily observations, Mage = 18 years in Wave 1 [W1], 75% female, 68% non‐White).\n\n\nResults\nHigher trait ERF in W1 was associated with less variable and unstable NA in W2, whereas higher state ERF in W1 was linked to less intense but more consistent PA experience in W2. In contrast, more intense NA in W1 was related to lower trait ERF in W2, whereas less persistent PA in W1 was related to lower state ERF in W2.\n\n\nConclusion\nCurrent findings are the first to reveal emotion and its dynamic patterns as both the regulator and regulation outcomes of flexible ER processes, yet with different patterns between NA and PA. Findings also emphasize the distinct nature between trait and state ERF that is associated with unique antecedents and consequences.\n\n"]