A significant body of scholarship in Physics Education Research (PER) has documented that students have intuitive knowledge resources that they use to make sense of the physical world. Similarly, for physicists, symmetry is fundamental to making sense of the universe. In this dissertation, I explore students' intuitive resources related to symmetry and how those resources are used when sensemaking about magnetism. Magnetism is a useful area for exploring this topic given the multiple types of symmetry present in permanent magnets. To situate this study, I use the overlapping theoretical frameworks of Knowledge in Pieces and Resource Theory. In these frameworks, the underlying assumption is that people have intuitive knowledge resources that they use to make sense of the world. The purpose of this study is to explore the intuitive knowledge resources students have that cluster around the notion of symmetry and to determine how students use these resources in reasoning about magnetism. The scope of this study is focused on middle and high school grade students engaged in a lesson where they generated and tested models of magnetism. Data capture and analysis were informed by the theoretical framework. I interviewed students in small groups using a semi-structured format, video and audio recorded the interviews, and collected the student written artifacts. Data analysis involved an iterative process of transcription and coding. The analysis is presented in a multiple case study approach to provide an in-depth understanding of the phenomenon. The findings indicate that students likely have four types of primitive resources related to symmetry. These resources are used across multiple types of symmetry in ways that are consistent with how physicists use symmetry. Additionally, I conducted a moment-by-moment analysis of an instance of using symmetry knowledge resources in sensemaking. Results are important for providing new insights about previously unexplored knowledge resources related to symmetry, in providing greater understanding about the way that students use symmetry productively in sensemaking about magnetism, and in providing guidance about ways to scaffold learning about magnetism. [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.]