Nuclear weapons are the most powerful and destructive weapons ever created. The combined power of all nuclear weapons currently in existence has the potential to destroy the World many times over. That fact has permanently changed the perception of warfare and created a whole new set of military and diplomatic concerns. This very short introduction explores these issues in detail, or at least with as much of a detail as the format allows. The book starts with a very brief explanation of how the nuclear energy works, and the realization in the late 1930s that it could be used for weapons. It follows with a condensed story of the Manhattan Project and the first nuclear explosions. The end of World War II, as the book argues, has only been a beginning of the new power relations based on the new reality that came with the gradual proliferation of the nuclear weapons around the world. The bulk of the book deals with the diplomatic and strategic policies that have marked the balance of powers during the Cold War. Even though the number of countries that acquired nuclear weapons never went beyond a single digit, there is a constant threat that many more regimes around the world would be all too willing to join the nuclear club. This had become an especially intractable problem upon the end of the Cold War. Instead of gradual disarmament, all of the nuclear powers have decided to cling to their arsenals. Even though deterrence might have been a major factor in the establishment and maintenance of peace throughout the twentieth century, the raise of non-state actors and their increasing predilection for the use of all sorts of weapons of mass destruction poses new and much more challenging threats for the world peace. All of these considerations are explored in this book, presented at a very accessible and relevant level.