The realities of shrinking fossil fuel reserves, growing global energy demand, and climate change concerns will force a change to a sustainable energy economy. Systems engineers need to take a leadership role in making the transition to this new energy economy. A study of large projects from the past provides some insights into methodologies that might be used to effect this transition; however, the complexity of the energy transition is far greater in some respects than on these earlier projects. The timeframe of this transition is measured in decades, the technologies involve numerous industries, and the spatial dimension involves the entire planet. Systems engineers will not only need new tools but will need to step into somewhat different roles than in the past. It is time to start planning for these new challenges, and INCOSE should play a key role in this planning.