Reappraisal and mindfulness represent two fundamentally different but interconnected ways of dealing with one’s emotions: whereas reappraisal is aimed at changing one’s thoughts and emotions, mindfulness is aimed atnotimmediately changing, but appreciating them. Despite this difference, prior research has shown that both are beneficial for one’s affective well-being. However, research on the spontaneous use of reappraisal and mindfulness in daily life found that they might be differentially associated with positive and negative affect, with reappraisal and mindful attention being more strongly associated with increased positive affect and mindful acceptance with decreased negative affect. Moreover, the spontaneous use of reappraisal may be less effective than mindfulness in daily life given that it is more cognitively taxing. To compare these possibly different benefits (i.e., change in positive and negative affect) and costs (i.e., feeling depleted), we re-analyzed two experience sampling studies (N= 125 andN= 179). Regarding benefits, endorsing reappraisal and mindful attention was significantly associated with increases in positive affect, whereas endorsing mindful acceptance was significantly associated with decreases in negative affect. Regarding costs, we found that endorsing reappraisal led to more depletion and that reappraisal was selected less often than mindfulness in daily life. Our results demonstrate the importance of assessing not only the different benefits but also the costs of emotion regulation in daily life.Supplementary InformationThe online version contains supplementary material available at 10.1007/s42761-022-00178-7.