Many consider conscience to be one of the most important, if not the fundamental quality that distinguishes humans from animals on one hand and machines on the other. However, what "is" conscience? Is it a product of our biological roots, as Darwin thought, or is it a purely social invention? If so, how did it come into the world?

Beginning in ancient Egypt Martin van Creveld explores conscience throughout history, ranging across numerous subjects from human rights to health and the environment. Along the way he considers the evolution of conscience in its myriad, occasionally strange, and ever-surprising permutations. Individual chapters are devoted to Japan, China, and the Nazis, as well as the most recent discoveries in robotics and neuroscience. The book concludes by arguing that, the claims of the artificial intelligence community notwithstanding, we are no closer to understanding the nature of conscience than we have ever been. As one computer expert has said, we shall probably build machines able to mimic conscience before we know what it really is.