There is a widely held conception that progress in science and technology is our salvation, and the more of it, the better. This, however, is an oversimplified and even dangerous attitude. While the future will certainly offer huge changes due to such progress, it is far from certain that all of these changes will be for the better. The unprecedented rate of technological development that the 20th century witnessed has made our lives today vastly different from thosein 1900. No slowdown is in sight, and the 21st century will most likely see even more revolutionary changes than the 20th, due to advances in science, technology and medicine. Particular areas where extraordinary and perhaps disruptive advances can be expected include biotechnology, nanotechnology,and machine intelligence. We may also look forward various ways to enhance human cognitive and other abilities using, e.g., pharmaceuticals, genetic engineering or machine-brain interfaces - perhaps to the extent of changing human nature beyond what we currently think of as human, and into a posthuman era. The potential benefits of all these technologies are enormous, but so are the risks, including the possibility of human extinction. This book is a passionate plea for doing our best to mapthe territories ahead of us, and for acting with foresight, so as to maximize our chances of reaping the benefits of the new technologies while avoiding the dangers.