This book exhaustively reviews the literature on the proposition that democracies do not fight one another, cautiously concluding that the idea remains supportable on empirical and theoretical grounds. The author opens a new phase in discussion of this issue, taking up the counterarguments that have been made since 1989. He seeks to show that there is a meaningful definition of democracy that excludes those cases, such as the Fashoda crisis, the American Civil War, or World War I, frequently cited to disprove the proposition. Ray points out that beyond the issue of the connection between democracy and peace is the question of how likely democracy is to spread. Like other theorists on this issue, he could have made much more of this point, drawing on the contemporary literature on democratic transitions. Much of the book will be heavy going for those not familiar with the existing academic research.