The conveying of mindfulness-based interventions in groups is the standard approach in inpatient settings. Understanding interaction processes that take place when patients exercise mindfulness-based interventions would be valuable for the improvement of patient care. Interaction processes during mindfulness-based interventions are best investigated by online-measurement and by a combination of multiple research methods to get a comprehensive picture of the many processes involved in relational aspects ultimately influencing the quality of the exprerience patients have. Previous studies demonstrated that humans synchronize during social interactions on various levels, i.e., heart rate variability, movements and even brain-activity of interaction partners mutually align with each other over time. The emerging synchrony has been shown to be a predictor of relationship quality, effective emotion regulation processes and even therapeutic alliance. Therefore, we collect data of patient dyads practicing a mindfulness-based intervention while assessing electroencephalogram (EEG), electrodermal activity (EDA) and heart rate variability (HRV) using a hyperscanning approach in combination with video and audio recordings as well as self-reported helpfulness of this patient-patient interaction. After recording, synchrony is quantified by analyzing the consistency of phase differences between the signals over time and the similarity between two signals as a function of time-lag. We assume that patient dyads synchronize on a physiological level and that synchrony is associated with self-reported helpfulness and sympathy. In addition, we will explore the association of synchrony of physiological measures and attachment, empathy, mentalizing ability as well as depression severity.