Equanimity is thought to be an outcome of meditative practices relevant to the regulation of emotions and behaviors. This chapter introduces the Equanimity Scale (EQUA-S), a self-report psychometric scale that proposes to measure levels of two dimensions of equanimity in the general population: Even Mindedness and Hedonic Independence. This scale has been assessed for reliability and validated in French (n = 265) and in English (EQUASE, n = 401). The studies demonstrated concurrent validity of the scale through positive correlations with some of the components of mindfulness (Nonreacting, Nonjudging, and Acting with Awareness from the FFMQ) as well as other measures of equanimity. It also shows negative correlations with neuroticism and avoidance and fusion scales. The EQUA-S has been used in general population samples and with experienced meditators, showing that the levels of both dimensions increase with mindfulness practice. Higher scores on both subscales of the EQUA-S are also related to more unbiased reactions in an approach-avoidance task. The Even Mindedness subscale has been shown to moderate the relationship between values obstruction and symptoms of depression, anxiety, and stress. Further studies are needed to understand the operational differences between equanimity, neuroticism, and emotional stability.