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. But how do we use these engineering tools in designing sustainable systems? This presentation will show how basic engineering principles, especially the concepts of mass and energy balances, can be used in characterizing the sustainability of engineered systems. Mass and energy balances will be applied at multiple scales to illustrate how even basic engineering concepts can give us powerful insights concerning the design of engineered systems. The presentation will conclude with an overview of how engineering educators, throughout North America, are incorporating concepts of sustainability into curricula.