The "Framework for K-12 Science Education" details ambitious goals for students' learning of science content and practices. However, this document provides science teachers little guidance about instructional practices that are central to helping students achieve these goals. Research indicates that a teacher's instructional practice can impact student interest and achievement more than advanced degrees or teaching experience and thus, identifying a core set of science teaching practices may be one key to improving science education. Based on a practice-based theory of teaching, this study used a panel of expert science teachers and university faculty to identify a set of core science teaching practices. The Delphi methodology used in this study engaged the expert panel in three anonymous and iterative rounds of voting and justification of science teaching practices. Nine of the fifty-one suggested practices met the pre-determined consensus criteria. Three major themes emerged from the results. First, a majority of practices, like "Engaging Students in Investigations" and "Facilitating Classroom Discourse," promote an interactive and dialogic science classroom. Second, the discussion among panel members across the three rounds indicates the need to develop a more common language and understanding of science teaching practice. Third, the panel highlighted the important role that on-going assessment plays in science teaching with practices like "Eliciting, Using, and Assessing Student Thinking about Science" and "Providing Feedback." This study lays the groundwork for the further decomposition of these core teaching practices and provides the foundation for further empirical research on how these practices are learned and executed by teachers, and their impact on student learning.