The world has seen a number of major energy transitions: from human and animal labor to burning wood, to burning coal, and then oil. Are we about to see another major change, or will the current renewables enthusiasm turn out to be just a blip on the screen? In this four-part series, I look at what historians and engineers can tell us about past and probable future energy sources. This first article examines the history of energy transitions and suggests lessons for the future. The second piece will focus on the current situation followed by ones on energy financing/investments and global warming.