The Multidimensional State Mindfulness Questionnaire (MSMQ) conceptualizes mindfulness as a mode of being or a state. The MSMQ reliably measures three facets of mindfulness at the within-person and the between-person level: present-moment attention, acting with awareness, and nonjudgmental acceptance. It thus complements similar multidimensional trait measures at the state level. The measure is highly economical (nine items in total, three per facet) and easy to understand for nonmeditators or mindfulness novices while preserving the theoretical foundation of mindfulness as a multidimensional construct. The MSMQ is ideal for the use in repeated measurement research approaches, such as experience sampling. Its facets are differentially related to positive and negative affect, reactivity to hassles, and emotion regulation strategy use at the within-person level in everyday life.