The main purpose of this project is to test whether Peer-Enhanced Motivational Interviewing (PMI) results in superior alcohol and marijuana use outcomes for emerging adults (EAs, ages 18-29) and their peers. Ninety peer dyads (total n = 180, ntarget client = 90, npeer = 90) are randomized to receive either Peer-Enhanced Motivational Intervie (PMI) or Waitlist Control (WC).