For a new energy generation technology, system, or fuel to be useful for society, it must provide more useful work, or energy, than it takes for its own existence. The quantity energy return on energy invested is one metric that is often used to compare energy technologies. The higher the energy return on energy invested, the more energy and work is available for society to prosper. However, as fossil fuel resources are extracted, those that are the easiest to reach with high energy return on energy invested are exploited first. U.S. resources estimated at energy return on investment (EROI) of 100:1 are now being extracted at nearly 10–30 to 1. A seemingly inevitable decline in energy return on energy invested exists for fossil fuels. However, for renewable energy technologies, such as photovoltaic systems and wind turbines, the energy return on energy invested seems to be increasing with technological innovation, but is still lower than for historical fossil fuels. On the other hand, our industrial system that produces renewable technologies currently depends on fossil fuels. How can industrial ecology and energy return on energy invested help us understand how to transition to more use of renewable energy? How high of an energy return can we expect both for individual renewable technologies and for the energy system as a whole? When, if ever, will the energy return on energy invested for fossil fuels and renewable systems be the same value, and what are the societal implications?