This article reviews the research support for Motivational interviewing (MI) so that practitioners can make informed decisions about the value and applicability of MI in their clinical work. We highlight the evidence from the three published meta-analyses of MI and a recent meta-analysis that we completed. MI is significantly (10%-20%) more effective than no treatment and generally equal to other viable treatments for a wide variety of problems ranging from substance use (alcohol, marijuana, tobacco, and other drugs) to reducing risky behaviors and increasing client engagement in treatment. Although most client-related variables are unrelated to outcomes (e.g., age, gender, severity), some decisions about treatment format (e.g., individual vs. group) are important. For example, relying solely on group-delivered MI appears to be less effective than one-on-one MI, whereas delivering MI with problem feedback is likely to generate better outcomes for some problems than MI alone.