Motivational Interviewing (MI) is an evidence-based practice that focuses on working through client ambivalence and increasing clients' motivation to change. The purposes of this study were to investigate the effect that a unique student-based training in MI had on counselor trainees' ability to perform MI, and on client outcomes. This training program consisted of one initial four-hour training session, two hours of follow-up supervision, and formal feedback via MITI 3.0 scores. Counselor-trainee skill was assessed via the MI Knowledge Questionnaire, the Helping Responses questionnaire, and the Motivational Interviewing Treatment Integrity code 3.0. In addition, the following instruments were used to assess client outcomes; attendance via observation assessments, the Session Summary, the Outcome Questionnaire-45.2, and the Client Satisfaction Questionnaire. The sample consisted of 43 graduate-level counselor trainees in their first or second semesters of practicum and 81 adult clients being seen in a university-based graduate student-training counseling clinic. Participants were purposefully assigned to either a treatment or control group. The counselor trainees in the treatment group received the unique training program, follow-up supervision, and feedback whereas the participants in the control group received a four-hour orientation to the student-training counseling clinic. There were four primary hypotheses proposed for analysis within this study (a) How does a brief training in Motivational Interviewing given to counselor trainees affect their ability to accurately perform MI?, (b) How does a brief training in Motivational Interviewing given to counselor trainees affect client functioning?, (c) How does a brief training in Motivational Interviewing given to counselor trainees affect client adherence?, and (d) How does a brief training in Motivational Interviewing given to counselor trainees affect client satisfaction with treatment? The statistical analyses of these variables yielded significant findings. Specifically, counselor-trainee skill in MI significantly improved in the treatment group as compared to the control group as assessed by the MITI with regard to the following variables: evocation, collaboration, autonomy/support, empathy, direction, MI non-adherent giving information, closed questions, simple reflections, complex reflections, total reflections, global scores, ratio of open questions, ratio of reflections, and ratio of MI adherent behavior. In addition, analyses revealed significant between group differences with client attendance. Specifically, between group-differences suggested that clients in the MI treatment group attended more sessions, missed fewer sessions, and completed therapy more frequently than clients in the control group. Detailed procedures and results as well as implications for the counseling profession and future research are explored within this study. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]