The expansion of norms allowing states to avoid, manage or resolve territorial disputes on land and sea has reduced the number of rivalries in the global state system, and increased the number of friendly inter-state relations, thus contributing to a more peaceful world. This is the main finding in Goertz et al's innovative book. The authors define peace as friendship between states, and its antonym is not war or violence but rivalry. War is just one expression of rivalry. Stalemate is another. The book moves our attention away from events such as wars, and directs it instead to the quality of inter-state relations. This ought to remove the need for the terms negative and positive peace, since negative means absence of war or violence, while positive means that plus something more. The authors want the ‘something more’ to be friendship between states, and use the terms negative and positive peace as synonyms for chilly and warm inter-state relations. The authors would have conveyed their findings better by staying away from redefining peace, and focusing uniquely on how growing cooperation between states has made the world more peaceful in the traditional meaning of the term. The book has some other limitations. It mostly ignores intrastate peace, except with regard to secession struggles and new state formation, topics analyzed with impressive rigor. Until page 209, it sees all states as equal, disregarding how great power rivalries could unravel world peace. And it does not quite grasp the basic difference between land and sea. Although its ambitious attempt to redefine peace is puzzling, it is a ‘must read’.