The positive impact of school libraries on student achievement is documented in a robust body of literature. Despite this evidence, the number of certified school librarians is declining nationally, and concerted advocacy efforts on the part of the American Library Association, the American Association of School Libraries and individual teacher librarians have been unsuccessful in reversing this trend. School librarians are being challenged to justify the very existence of their programs. This study explores the use of social capital to enhance the power and influence of school librarians, and explores its potential to improve advocacy outcomes. The findings fill a significant gap in the social capital literature by expanding its breadth to include the field of Library and Information Science. Narrative inquiry methodology was used to conduct semi-structured, in-depth interviews of 29 school library system directors in New York State, with subsequent coding and thematic analysis of interview transcripts. Additional surveys were administered to capture demographic information and to illuminate technical aspects of social capital development, utilization, relevance, and value within school library systems in New York State. School library system directors identified social capital as an important tool in maintaining funding, preserving staffing and programs, and in influencing decision-makers, although many were unfamiliar with social capital theory. While directors recognized barriers to social capital development on individual and system levels, the majority promoted social capital utilization as a means of enhancing traditional advocacy practices and provided evidence of its effectiveness. These findings confirm that teacher librarians and school library leaders are ideally positioned to harness the power of social capital by forming relationships with decision-makers. By shifting the power paradigm of K-12 education, teacher-librarians and school library leaders may ensure the long-term sustainability of school libraries. [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.]