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ii Functional representations are often used in the conceptual stages of design because they encourage the designer to focus on the intended use and purpose of a system rather than the physical solution. Function models have been proposed by many researchers as a tool to expand the solution search space and guide concept generation, and many design tools have been created to support function-based design. These tools require designers to create function models of new or existing artifacts, but there is limited published research describing what types of functions should be included in a model or the appropriate level of abstraction to model artifacts. Further, there is little experimental evidence that function models are useful for concept generation. Therefore, this research focuses on how artifacts should be modeled to support ideation in conceptual design. In this research, three functional representations are studied: function models, interaction models, and pruned function models. First, a user study is conducted to tes