A challenge for public schools is to successfully support and professionally develop early career teachers and thereby prepare them for long and successful careers in education. Multiple studies have indicated high levels of turnover in the profession of teaching, especially during the beginning years in a teachers career. The purpose of this qualitative research study was to describe how eight early career secondary mathematics and science teachers perceived and made sense of their experiences navigating multiple professional communities and interacting with mentors designed to improve retention. Topics examined included the contextual elements that influenced the early career teachers interactions with mentors and professional communities; how they positioned themselves within multiple professional communities; and how they perceived these experiences influenced the development of their teaching practice. An extensive semi-structured interview of the early career teachers generated data that were analyzed to identify emergent themes and patterns. The findings of this study indicated navigating professional communities and interacting with mentors influenced the early career teachers decisions to adopt important components of a learner-centered approach to teaching such as engaging students in active learning processes, utilizing formative assessment, promoting cooperative work, and interacting with students on an individual level. Also, access to professional communities and mentors afforded the early career teachers a level of relief of their anxieties related to being a new teacher, a boost of confidence in their teaching abilities and judgments, and an outlet to share stories and experiences, which decreased their feelings of professional and social isolation. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]