This paper defines professional certification as a voluntary process regulated by a profession to measure competencies possessed by its practitioners. A hierarchy of motives for certification is illustrated, and its importance for the fields of adult education and human resource development (HRD) is emphasized. The evolution of the concept of professionalization is presented from four perspectives: philosophical, nontraditional, characteristic, and developmental. Adult education and HRD's status as professions is examined, and the attempts of these fields to develop a fully accepted body of knowledge, a set of practitioner competencies, and a program of professional certification are described. The paper addresses such certification issues as type of administrative approach, identification and validation of competencies, evaluation criteria, grandfathering, recertification, and revocability. Also discussed are positive implications (enhancement of the profession, recognition and increased earning potential for practitioners, and standardization) and negative implications (fragmentation, financial and human costs, and legal difficulties). Finally, the following nine-stage model for developing a professional certification program is presented: (1) identification of purposes or motives, (2) identification of essential competencies, (3) establishment of procedures, (4) identification of prospective candidates, (5) response to identified issues, (6) establishment of criteria, (7) marketing of the program, (8) evaluation and modification of the program, and (9) remarketing of the program. A four-page list of references concludes the document. (SK)