Despite advances in understanding emotion regulation (ER) flexibility (e.g., flexibly using ER strategies to meet situational demands), there is heterogeneity in conceptualizations. To address this, we provide a unifying operationalization for ER flexibility and a person-specific ER flexibility framework. We define ER flexibility as the ability to continuously monitor the effectiveness of chosen ER strategies to meet one's goals for a situation and to adjust strategies, as needed, in response to changes in internal states (e.g., affect, beliefs about emotions) and external contextual demands (e.g., regulatory goals, situational factors/demands). This paper discusses existing ER flexibility frameworks, their empirical research, and potential limitations. We then present our person-specific ER flexibility framework. We highlight methodological applications, future research directions, and limitations.