Self-presentation plays an important role in developing one's sense of self. Nowadays, young people's self-presentation extends from face-to-face contexts to social networking sites (SNSs). SNS self-presentation may change when youth transition into to college, faced with the need to reclaim or redefine themselves in the new environment. To date, there has been little effort to explore these potential changes in youth's SNS self-presentation across the transition, and to examine associations between online self-presentation and development of one's sense of self. Drawing on the psychological approach to identity and symbolic interactionism, the longitudinal, mixed-methods study aims to bridge the gaps. A panel of 218 freshmen at a major university in the Midwest was surveyed once at the beginning of students' college career and again at the end of their first semester. A subpanel of 28 students also participated in interviews at the same two times. Findings showed that freshmen's Facebook self-presentation became less restricted at the end of the semester. In addition, presenting broader, deeper, more positive, and more authentic self-information elicited more supportive feedback from the audience, which contributed to higher self-esteem contemporaneously, though not longitudinally. Putting more thought into Facebook self-presentation engaged students in self-reflection, which benefited their self-esteem several months later, although intentional posting and self-reflection appeared to be part of a ruminative process that clouded self-concept clarity concurrently. Implications for future research and practical work are discussed. [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.]