The evaluation of higher education systems is regarded as one major requisite for the growth and development of such systems; hence, the continuous improvement of the quality of higher education needs the establishment of a quality assurance sub-system and the use of scientific methods in this field. According to the global experiences, the way higher education institutes participate in quality assurance activities is in a voluntary-mandatory scale. The major difference among quality assurance systems is whether their participation is voluntary or mandatory. The present research studies 70 evaluation and quality assurance agencies in 60 countries, in terms of the compulsory and voluntary essence of their quality assurance processes. It employs the qualitative methodology based on a documentary analysis. To this end, the documents, data and information obtained from scientific-research articles, books, and research reports have been analyzed together with the experiences of those agencies in charge of accreditation and quality assurance in higher education. The results show that quality assurance processes are mandatory in 64 % of the agencies and 27% of them follow a voluntary approach. Moreover, in 9% of agencies, both the voluntary and mandatory processes are implemented.Accordingly, considering the significance of the performance and role of higher education and its impacts on sustainable development, it seems that quality improvement requires a comprehensive quality evaluation system, involving both voluntary and mandatory approaches, based on the participation of higher education institutions.