<p>Cultivating cross-disciplinary understanding across science and engineering instruction will be essential to preparing the next generation of scientists to prosper in an increasingly interdisciplinary STEM workforce. This study reports on the culmination of a project that has been aimed at addressing this challenge by investigating how science and engineering students use the first law of thermodynamics, a guiding principle of the crosscutting concept of energy and matter, to transfer across disciplinary boundaries. A qualitative interview study was undertaken in which chemistry-, engineering-, and physics-major students were recruited and tasked with addressing familiar and unfamiliar first law problems that incorporated the systems, language, and notation of each respective discipline. Guided by the dynamic transfer framework, data were analyzed via a general inductive approach to categorize the contextual resources, or target tools, students leveraged to address the provided problems. This analysis revealed three unique guiding epistemologies whose frequency and character of emergence signify field-specific approaches to transferring into an unfamiliar disciplinary context. Connections are drawn to highlight the capacity of the derived findings and developed methodology to support cross-disciplinary understanding in the classroom and in future transfer of learning research.</p>