Mathematics is generally considered to be a fundamental element of engineering education. However, there is little empirical evidence characterizing the role of mathematics in the engineering design process. The goal of this paper is to take a research informed approach towards understanding engineering students' use of mathematical problem solving strategies while engaged in capstone design projects. This paper presents some initial evidence elicited through observation of a team of five industrial engineering seniors, interviews with these students as well as students from other engineering departments and document analysis. The data is analyzed using a framework based on the work of Alan Schoenfeld1 which consists of five aspects of mathematical thinking: the knowledge base (e.g., calculus), problem solving strategies or heuristics, effective use of one's resources (or cognitive structures, such as memory), beliefs and attitudes (about mathematics), and engagement in mathematical practices. Results from this study provide insights for mathematics and engineering educators as they support engineering students' integration of mathematics and mathematical thinking into their design practices.