If there is anything that you can rely on throughout history, it is that there will be warfare. Warfare is the subject of intense study, as it should, because ultimately lives and civilization depend on the outcome of warfare. History is written by the victorious. There are classic works which discuss the essence of warfare such as "The Art of War" by Sun Tzu and "On Warfare" by Carl von Clausewitz. This book describes the categories of warfare from insurgency to cold war, from civil war to world war and the many other variations including terrorism, asymmetric warfare, war by attrition, nuclear war, network-centric warfare and cyber warfare. The combat theater is also discussed in sections on unconventional warfare, aerial warfare and naval warfare. Tactics such as joint warfare and psychological warfare are also addressed. This book provides an insightful overview into the world of warfare. It has been said that 'only the dead have seen the end of war' and that 'the best offense is a strong defense'. To those who protect, serve, fight and make the ultimate sacrifice - war is but a bitter reality. Hopefully the study of warfare and the awareness of its causation can serve as the best prevention of future wars and conflicts, resulting in prevention by diplomatic and political means. This book reveals the categories of warfare so as to serve as a source of information to those who engage in its prevention, from the voter to the politician.