This book, pulling together the mature reflections of a Czech-born Canadian who has devoted nearly four decades to studying energy, is a thorough introduction to the subject and a thoughtful consideration of the conundrums it presents. Smil skillfully guides readers through the forest and the trees. Energy is above all a quantitative subject -- an idea that is good in principle can be quantitatively insignificant -- and this book is not for the numerophobic. But given the pervasive importance of energy, Smil conveys well the complexity and uncertainty of the energy system and its social and environmental impacts. (An especially instructive chapter recounts the dismal record of long-term energy forecasts.) Still, Smil believes that current energy practices cannot continue indefinitely, not because fossil fuels will be exhausted but because the environmental impact of their use will become increasingly unacceptable and even dangerous. He sees promising technical and economic potential for change but is pessimistic when it comes to the possibility of intelligent, concerted action in that direction.