Management scholars have predicted for over a decade that mindfulness could enhance work performance, yet supporting evidence has been elusive. However, mindfulness was initially theorized as a functional response to stress. Reconnecting mindfulness to stress may help better explain when and why mindfulness could improve performance. We are the first to test the idea of on-the-spot mindfulness – meditating in specific situations in which people are highly stressed for 8-15 minutes to change their psychological state, approximately twice per week. We build a theory of on-the-spot mindfulness and how it can improve employees’ performance (work performance and customer service quality) and civility (helping behaviors and less counterproductive work behaviors). We expected it to do so by cuing an internal locus of control. We tested our hypotheses in an 8-week field experiment among 466 employee-supervisor dyads using multiple meditation conditions, control conditions, well-being manipulation checks, and supervisor-rated measures of the dependent variables. Our hypotheses were mostly supported (i.e., in 81%-94% of the contrasts of interest between treatment and control conditions). We discuss the relevance of on-the-spot mindfulness for the management and psychology literatures, as well as for management practitioners.