Sustainable design defined broadly is the problem of designing environmentally benign products so that the environment can be maintained with minimal negative effects from the product throughout the products entire lifecycle. This research investigates how sustainable design can be achieved at the conceptual design stage. Although sustainability encompasses a vast number of issues ranging from energy efficient solutions, design for disassembly, recycling, proper material selection, and improved manufacturing choices, the research focus of this work is on the particular issue of product evolution as it relates to the flexibility of a product or concept. Product evolution, often powered by new technology, erases the market competitiveness of concepts over time and impacts flexibility on the design effort side. Specifically, how does the designer develop concepts that can at least partially be reused and adapted to the next product generation with minimal effort? One answer is to design flexible concepts that can incur unknown future changes with maximum concept reuse. Flexibility in this context implies the property of a concept, physical solution, component, or product, to be robust and tolerant to generally unavoidable evolutionary changes. The challenge is to know how to configure a product to satisfy this requirement. As part of this research, we perform empirical studies of product evolution to determine evolutionary trends. Product evolution is measured in the broad terms of product performance over time. The goal is to predict when a product should evolve by either 1) moving from the lower plateau of an S-curve to the higher plateau or 2) jumping to a new S-curve being prepared to do so in a sustainable manner. That is, the objective is to allow companies to be able to reuse components or platforms (including reconditioning and recycling), tooling as well as design and manufacturing staff. The key toward this goal is an understanding how products evolve and what conditions coincide with product change. The approach is to investigate the types of changes (evolutions) that lead to flexible (sustainable) designs. The results of this research can be used for a prescriptive approach in developing a sustainable design method that relies on this newly acquired knowledge of product evolution.