Recent science education reform has emphasized teaching science as practice -- striving to engage students in the authentic work of scientists so they gain deeper understanding of scientific knowledge and how that knowledge is established. To make this vision of science education a reality in classrooms, teachers must be well prepared to teach science as epistemic practice. Prior work suggests that teachers need more support and preparation to create environments within their classrooms that reflect and help students learn to participate in the practice of the scientific community. To address this issue, we investigated teachers understanding and instruction for science as epistemic practice in middle school classrooms. We explored (a) how teachers' instruction aligned with the epistemic practice of science to help build scientific communities in their classrooms and (b) how teachers understood and reflected on their own teaching as supporting participation in the epistemic practice of science. We used the Apt-AIR framework of epistemic practice (Barzilai & Chinn, 2018) as a theoretical lens to describe science as epistemic practice, to establish what participation in this practice looks like in classrooms and what students should learn about the epistemology of science, and to analyze teachers' instruction for science as epistemic practice. We used videos of classroom instruction to investigate how teachers integrated aspects of scientific practice in their teaching and how patterns of their instruction related to students' understanding of and participation in science as epistemic practice. We also examined teachers' conceptions of scientific practice through reflective interviews about their own teaching. This research provided novel approaches to investigating how the connected nature of scientific practice is reflected in teachers' instruction and students' understanding. Findings revealed features of effective science instruction, specifically that teachers making strong connections between and talking consistently over time about aspects of practice can support students to understand and successfully participate in scientific practice. Additionally, our findings suggest that teachers may not be intentional to teach science as epistemic practice and raise critical challenges for making a focus on practice more central in science classrooms. [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.]