Architecture practice is on the front line directly applying best-case evidence-based solutions to conserve energy. Conserving resources through energy efficiency rely on energy modeling software to simulate performance, evaluate energy use, and optimize energy savings in building designs. Today’s powerful building performance simulation tools can be leveraged for energy modeling during early design phases. To further reduce building energy consumption, energy simulations done during conceptual design has potential to impact longterm energy use in architecture. This paper reviews early or conceptual building energy modeling research identifying what is simulated when in building design, provides design examples that utilize evolutionary modeling and proposes recommendations for further energy simulation research in early design.