Engineers interact with their products and processes largely through models, however rarely reflect about the nature of these models and how technical possibilities and actions are affected by the models' properties and characteristics. Models in engineering describe the product as well as its generating process, but at the same time also shape and create them. This clearly distinguishes them from scientific models that primarily aim to describe a certain target system. While over the last decade, there has been a growing body of literature on models in the sciences, much less research has been done on models in engineering design. In this chapter we aim to fill this gap by taking a closer look at models in engineering design from an epistemic point of view. In particular we suggest a classification of different types of models used in engineering design and compare them to models used in scientific research. Thereby we do not aim at an encompassing map of models in engineering practice, but we aim to identify key categories of models with regards to their relationship to their targets. We contend that the functions of models in engineering design cannot be fully captured when focusing on the representative aspects of models alone as done in contemporary philosophy of science.