Prior Learning Assessment (PLA) is a term for various methods by which universities accredit student experiential learning. One such method is the academic portfolio, a written reflective process in which students demonstrate that their personal or professional learning fulfills university outcomes. Proponents of academic portfolios claim that they also improve student critical thinking and problem-solving abilities. Research on traditional undergraduates suggests that differences in critical thinking and problem-solving are related to epistemological development, but little research has been done on adult undergraduate epistemologies or how student epistemology may affect PLA portfolio work. This study attempts to answer two questions: (1) To what extent are there differences between the epistemological beliefs held by adult undergraduate portfolio students as compared to adult undergraduates who take only traditional courses? (2) What are the experiences of adult portfolio undergraduates regarding tacit knowledge articulation and what impacts does this articulation have on their personal epistemologies during the portfolio process? The study follows a sequential mixed methods design, utilizing the Epistemological Beliefs Inventory (EBI) and an open-ended interview to answer the research questions. A total of 82 undergraduate students participated, all of whom were 25 of age or older. Findings suggest that successfully completing a PLA portfolio may facilitate epistemological development specifically in the areas of problem-solving and critical thinking. However, it is possible that the epistemological beliefs of those who complete portfolios may not differ substantially from those held by adult undergraduates who do not engage in portfolio work. Additionally, even students who complete portfolios successfully may find the process unclear and frustrating for reasons that may be related to their epistemological beliefs. Although more research is needed on adult epistemologies and how the PLA portfolio process may affect them, PLA professionals should understand and consider student epistemological beliefs when developing portfolio processes and advising students. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]