This exploratory qualitative study examined science teacher enactment of crosscutting concepts (CCCs), a core aspect of Next Generation Science Standards (NGSS) three-dimensional learning, which also includes disciplinary core ideas and science and engineering practices (SEPs). We collected naturalistic observational and interview data from 13 California teachers involved in a major NGSS implementation initiative and analyzed this data by applying four roles of the CCCs in instruction as described by Rivet et al. (2016). The roles these conceptual resources play are: lens, bridge, tool, and rules of the game. Using this schema, we provide thick description of teachers' different purposes for, modes of, and challenges in using CCCs in their instruction. Naturalistic observations provided information about how teachers were using CCCs in their classrooms while interview data revealed the opportunities and challenges teachers perceived in CCC enactment, both of which are little addressed within the emerging body of CCC research. Teachers received extensive professional development (PD) on the NGSS but nevertheless identified CCC enactment as particularly challenging. For this reason, we suggest the four roles of the CCCs, which were indeed reflected in our data set, could be a helpful framework for making the CCCs more accessible and understandable to teachers, and thus more likely to be incorporated into everyday science instruction to enhance student learning. We envision future use of this framework as an epistemic heuristic having the potential to bring more clarity to CCC enactment for researchers, teachers, curriculum developers, and PD providers.