This project randomized peer dyads, consisting of one EA (Emerging Adult; 18-29 years old) with a substance use problem (i.e. target client) and one peer, to one of two conditions. In the Peer-Enhanced Motivational Interviewing (PMI) condition, target clients and peers will receive separate one-hour sessions of Motivational Interviewing (MI) , an empirically-supported treatment that helps individuals work through ambivalence about making changes in substance use. MI is thought to work because it is a non-confrontational intervention where a therapist empathetically reviews substance use behaviors, listens empathetically, and reinforces any client statements indicating a desire to change. With the 'peer' of each PMI dyad, the therapist presents peers with data about the extent of the target client's substance use, builds the peer's motivation to help their friend, and teaches the peer communication skills they can use to influence the target client's substance use. In the WC condition, target clients and peers can receive PMI after the study follow-up period. Both target clients and their peers are followed for 12 weeks post-intervention.