Electromechanical products and systems are often designed to transform or reconfigure between two or more states. Each state is customized to fulfill a specific set of functions, and the transformation between these multiple states allows for greater functionality and the elimination of many trade-offs between conflicting needs. Empirical examination of existing transforming systems and their similarities has led to a foundational transformation design theory, with meta-analogies and guidelines that explain how transformation processes occur, when they are useful, and how the designer can ensure their maximum benefit. The foundation of these principles and guidelines forms a meta-analogical framework for designing transformers and transformational systems. This paper presents a history of the development of transformational design theory, including the relationship of the research to case-based reasoning in other fields. Ideation methods are presented that specifically exploit the meta-analogies, i.e., categories of transformers. An example design problem is considered to illustrate the potential utility of this design-by-analogy approach.