While research indicates that MBRP is effective in reducing substance use relapse, only preliminary research has examined the influence of MBRP on the physiological mechanisms involved in emotion regulation after exposure to stress. Examining these physiological mechanisms is essential because the central and autonomic nervous systems work together to coordinate the self-regulation of attention, cognition and emotion when stressful cues are encountered, such as when a substance dependent individual is exposed to stressful and/or substance related stimuli. Heart rate variability (HRV) is generally seen as an index of emotion regulation. High frequency HRV reflects parasympathetic activation of the autonomic nervous system and the body's ability to exert cognitive control over attention and emotional responding. Higher levels of HRV are associated with greater emotional and behavioral flexibility, and tend to be associated with better mental and physical health outcomes. In contrast, lower levels of HRV are associated with a wide range of medical and psychiatric disorders, including acute and chronic alcohol ingestion, anxiety and depression. Among alcohol dependent individuals, mindfulness training has been found to increase HRV and lower subjective levels of psychological distress in response to stressful cues in the short-term. The proposed study will be the first to examine the long-term effects of MBRP on HRV and self-reported psychological/behavioral functioning. The results will provide a better understanding of the interplay between the psychological and physical mechanisms involved in relapse and help determine whether MBRP has lasting psychological and physiological benefits. In other words, assessing both the psychological and physiological effects of MBRP will provide a more accurate and comprehensive understanding of how mindfulness aids in promoting self-regulation and relapse prevention. Finally, little is known about which types of individuals are most likely to benefit from MBRP. It is necessary to examine individual characteristics (i.e., baseline levels of HRV, trait mindfulness, substance use, anxiety, depression) to determine which characteristics are associated with positive treatment outcomes in both the short and long-term. This knowledge will enable more efficient and effective delivery of the MBRP treatment.