How do we design a sustainable built environment for ten billion people? What policies, economic structures and social structures will move us in this direction? These are questions that challenge contributors to and readers of this journal. They are also questions that challenge engineering educators, training the designers who will create the built environment of the twenty-first century. Engineering educators often describe their curricula with the metaphor of a toolbox. Engineering principles of mass conservation, energy conservation, and thermodynamics, to name just a few, can be viewed as powerful tools for solving problems and designing processes and products. An engineering education makes students proficient users of these tools. Yet if the toolbox is too limited, the designs created using those tools can be ineffective. To repeat an overused cliche, if the only tool you have is a hammer, everything looks like a nail. An engineering education also teaches our future designers to focus. From the earliest stages of an engineering education, students are taught to draw a ‘‘box’’ around the system to be analyzed, and to limit their attention to that boxed system. This is a necessary and powerful concept in engineering education, yet there is an increasing need to teach students to consider factors that are ‘‘out of the box’’. Engineering education needs new approaches that enlarge the box, and that give students the tools to effectively treat more complex problems, like the design of sustainable systems. How can engineering educators, practicing engineers and designers of all sorts, enlarge the box and create new tools? There are no simple answers, but offered here are some basic thoughts, using tools needed for the design of sustainable technologies as an example. As a case study of the process of enlarging the box and creating new tools for engineering design, consider the decisions surrounding how to provide personal mobility. In most of North America, personal mobility is achieved through the automobile. The choice of the automobile as the provider of personal mobility necessitates other decisions involving land use, fuel infrastructures, industrial supply chains, and societal investments in roadways. These levels of impact, associated with mobility decisions, are shown conceptually in Fig. 1. A first set of design questions (represented by the innermost layer of Fig. 1) are the choices faced by a parts engineer. In selecting the materials for a bumper/ front end, for example, the engineer could select galvanized steel or a composite, glass-reinforced plastic. Which bumper is better? Like many engineering decisions, this decision can be viewed from environmental, economic and social perspectives. The galvanized steel can be far more effectively recycled, yet the plastic composite will lead to greater fuel efficiency over the life of the vehicle. The steel bumper may be less costly to repair, resulting in different costs of ownership than the glass composite bumper. And, there may be different levels of passenger safety offered by the two materials. New analysis tools, such as environmental life cycle assessments (Curran 1996), have emerged to allow designers to address some of the multifaceted attributes of their designs. These types of analysis methods should become part of the engineer’s toolbox. The next level of questions and tools, represented by the second layer from the center in Fig. 1, considers supply chain impacts. For automobiles, how are parts manufacturers, automotive repair shops, coal producers, The authors have jointly formed the Center for Sustainable Engineering (http://www.csengin.org), which is dedicated to the development and dissemination of educational materials for incorporating concepts of sustainability into engineering curricula.