Private higher education (PHE) worldwide has been a rapid development in the last several decades. The private sector will continue to grow, diversify and undoubtedly play a significant role in the political economy of higher education. Nevertheless, systematically empirical studies on the trio relationships among PHE, institutional diversity and political economy are still miniscule, especially outside the U.S. In Thailand, studies on even public higher education utilizing international literature are rare, as is research with a macro-level empirical analysis of private-public comparison. Thus, this study focuses on the fundamental differences among Thai private higher education institutions (PHEIs) and between private and public ones and the extent to which political economy influences their shapes and differences. The study attempts to determine and demonstrate whether, how and how much the Thai case fits Levy's (1986b) PHE pioneering concepts on types of PHE: religious-oriented, semi-elite, demand-absorbing. The study employs combined methods of analysis: content analysis of 24 interviews of private university presidents and national policymakers and institutional data and legislative documentation, descriptive statistical analysis and Ragin's (2000, 2008, 2009) Fuzzy-Set Qualitative Comparative Analysis (fsQCA). The findings show clusters of characteristics on governance and finance in relation to different institutional types. Intra-sectorally, Thai PHEIs are different among themselves based on types of ownership and characteristics previously identified in the literature. Levy's theory is vigorously applicable to the Thai context. Nonetheless, several deviations appear. The findings introduce a new category, serious-demand-absorbing, which incorporates elements from other types. The findings also suggest that institutional isomorphism happens due to all PHE types tending to share comparable characteristics in both governance and finance and that institutional diversity becomes a matter of degrees. Institutional functions, e.g., size, age, mission, fields of study are catalysts in differentiation or isomorphism of different PHE types. Inter-sectorally, private and public higher education institutions are most different from one another in the law governing them, internal administration style, and government funding. Finally, political economic policies, e.g., quality assurance, the PHE Act, and student loans result in coercive isomorphism while aggressive market competition bolsters institutional diversity. [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.]