Established in 1976, SOPA was an association of professional practitioners of archaeology in North America. There were two categories of affiliation: Certified Member, and Certification in one or more areas of emphasis without membership. Before Certification and/or Membership was granted an individual's qualifications were assessed. The basic responsibilities of SOPA were to define professionalism in archaeology, to provide a measure against which to evaluate archaeological recommendations and research, and to furnish a forum for a challenge to such recommendations and research. All Certified Professional Archaeologists, whether Members or not, agreed to adhere to a code of ethics and standards of research performance. SOPA published an annual Directory of Certified Professional Archaeologists and a Newsletter. After 22 years of operation, however, SOPA was wound up and transformed into the Register of Professional Archaeologists.