The purpose of this qualitative case study is to identify how PLCs influence the high school English teachers' practice in response to key instructional shifts within teaching standards in the Southwest United States. Legislation from the last two decades puts expectations in place that raise the bar for American students and their teachers through standardized testing and standards-based instruction. Under the pressure to prepare students for college and career readiness, embedded and practical professional development is vital. This study emphasizes how teachers work together utilizing DuFour's Professional Learning Community model to support the implementation of three instructional shifts outlined in CCSS. The primary research question of this study is "How do Professional Learning Communities (PLCs), as a means of professional development, influence a shift in teacher practice in response to key instructional shifts?" Using purposeful sampling, this qualitative case study included participation from thirteen high school English teachers at one school site. Data was collected from three sources: PLC observation, one-on-one semi-structured interviews, and artifact collection. Thematic analysis was applied to the data in response to the four research questions. Emerging themes from the results show that that the PLC supports teachers implementing three key instructional shifts in English Language Arts through sharing assessments, resources and instructional practices. [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/en-US/products/dissertations/individuals.shtml.]