Beliefs about emotion are clearly relevant for emotion regulation and psychopathology. Yet, understanding the dynamics of emotion beliefs (i.e., the situations and contexts in which beliefs may change over time) remains an important avenue of investigation. The current ecological momentary assessment study (n = 102) assessed nine different beliefs about emotion across a variety of contexts (location, activity, social context, consuming alcohol, eating food, drinking caffeine, subjective emotional experience, feeling invalidated, feeling tired, feeling creative). When participants reported feeling subjectively worse than usual, they also reported their emotion regulation strategies. Results revealed that all of the beliefs except beliefs about longevity (i.e., beliefs that emotions will last “forever”) were associated with at least one contextual factor. In addition, when people reported greater longevity beliefs, they also reported asking “why” (i.e., rumination), attempts to distract themselves, and escape behaviors. Results confirm that beliefs do vary by context, and within-person fluctuations in beliefs are associated with momentary emotion regulation strategies.