Motivational interviewing (MI) is a method of eliciting individuals’ inner motivation to change their behavior. MI is typically delivered within health care settings as well as in occupational and educational settings and in multiple populations. MI builds on practice skills that are relational and technical, aiming to evoke and reinforce client utterances in the direction of behavior change, termed change talk, and to reduce client utterances in the direction of maintaining current behaviors, termed sustain talk. Meta-analyses show that MI training leads to increased practice of relational and technical skills, and practice of relational and technical skills are related to change talk. Technical skills increase the proportion of change talk in relation to sustain talk. Sustain talk has a negative effect on behavioral outcomes, but change talk has a positive effect on behavioral outcomes. Meta-analyses also show positive effects of MI over six months in reducing or eliminating binge drinking, alcohol consumption, problematic substance use, and smoking, and increasing physical activity in chronic illness patients. Studies have shown positive effects of MI on behavior change in a range of behaviors and populations. A step-by-step guide to MI outlines typical intervention content, target populations and behaviors, practitioner training and skills required, and evaluation of fidelity and effectiveness.