Emotional well-being (EWB) is an important component of mental and physical health that includes both positive emotions and an absence of emotional symptoms (e.g., depressive- and anxiety-related). EWB has declined dramatically among college students, a trend only exacerbated by the COVID-19 pandemic. We need to develop solutions that can improve college students’ EWB and can be applied under physical distancing conditions. In this study, we propose one such solution, an internet-delivered mindfulness-based intervention (MBI). We hypothesize that it will increase EWB, including a reduction in negative emotions and an increase in positive emotions. We will also investigate a key purported mechanism, namely improved social well-being and associated social behavior. We will conduct a randomized controlled trial (RCT) wherein participants will receive a 2-week smartphone-based MBI or a structurally equivalent coping control intervention. EWB will be assessed at pre-intervention, post-intervention, and follow-up through ecological momentary assessment (EMA) and self-report questionnaires. EMA assessment of felt connection and loneliness, along with passive smartphone sensing will be used to determine how changes in experience and behavior contribute to MBI success. Finally, we will investigate participants’ subjective experiences in using the interventions through content-coded interviews, which will help to refine internet-based mindfulness (and other) training.