The Posse program was designed to support diverse student populations to successfully engage in undergraduate education and flourish as both professionals and as community leaders. The UW-Madison Posse program focuses on the development of STEM scholars and leaders. This study studies the experiences of Posse alumni to better understand how the features of the program contribute to their post-graduate lives and careers. Specifically, the study explored how socialization, community, relationships, and institutional opportunities within the program and university played a role in the retention, persistence, and transition of these alumni into the STEM workforce. The study found that when alumni had a sense of belonging, a community, and support systems their confidence and self-worth was positively impacted. The study found that mentorship played a key role for participants during their undergraduate journey. Alumni utilized the relationships formed, developed vital networks, grew valuable skill sets, gained hands-on experience, and executed professional development strategies that greatly impacted their life after college into the STEM workforce. Ultimately, participation in the Posse Program proved to be largely impactful for successful degree obtainment and transition into their chosen STEM field and career. [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.]