This mixed-methods research project investigated how active-duty Marines used social media sites to engage in self-directed professional development and personal support activities in response to their military identities and experiences. Quantitative data was collected through surveys with 200 active-duty Marines. Survey results were further illustrated through follow-on interviews with survey participants that corresponded to self-guided tours of their military-connected social media groups. Through the creation of private, unofficial, military-connected social media groups, and their communication within these groups, Marines demonstrated learner agency that supports their success within the Marine Corps and also prepares them to transition from the military into new professional and academic communities. These findings indicate new opportunities for institutions like the Marine Corps and higher education to enhance the continuum of support to Marines during and after their military service, as well as new opportunities for scholars to investigate the learning strengths that service members and veterans bring to higher education. [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.]