Prototyping can be seen as the heart of the innovation process. Typically, engineers and designers both work on prototyping activities, but their diverse backgrounds make for different perspectives on prototyping. Based on earlier literature, this study investigates commonalities and differences in the prototyping behavior of engineers and designers.For this study, semi-structured interviews and workshops with different experiments were conducted. Using low-fidelity prototypes, our results indicated that there are differences in the early phase of prototyping. Engineers focused on the features and functions of a prototype and needed to meet specific goals in order to push the process forward. Designers, on the other hand, used prototypes to investigate the design space for new possibilities, and were more open to a variety of prototyping materials and tools, especially for low-fidelity prototypes. In the later prototyping phases, the prototyping behaviors of engineers and designers became similar. Our study contributes to the understanding of prototyping purposes, activities, and processes across disciplines, and supports the management of prototyping in new product development processes.