This chapter reviews the 18-item Relaxation-Mindfulness Scale for Adolescents (EREMIND-A), which was created primarily to evaluate effects of the mindfulness-based interventions (MBIs), tailored for adolescents in an educational context, that emphasize relaxation and insight aspects of mindfulness. It first covers theoretical foundations of the measure followed by its development and validation. Importantly, psychometric properties of the EREMIND-A scale are described and critically evaluated, and the current scale version is included together with the scoring information at the end of the chapter. The scale creators reported acceptable psychometric properties of the scale including three factors: concentration of attention on the present moment, insightful sensory awareness, and relaxation abilities and attitudes. However, despite promising psychometric properties, there is lack of validation studies, and translations of the scale into different languages, meaning that such studies are warranted.