This book is about strategic coordination – both strategic voting and strategic attempts to regulate entry – in the world's electoral systems. I assume that readers are familiar with the concept of a coordination game. Those who are not, and are not satisfied with the brief description given below, may wish to consult Lewis (1969), Schelling (1978), or other sources.

The basic idea of a coordination game is simple enough and can be conveyed by considering a classic illustrative game, the Battle of the Sexes. In this game, a man and a woman must independently choose whether to attend a prize fight or a ballet performance. The man prefers the prize fight to the ballet, while the woman has opposite preferences. Both, however, are primarily concerned with having each other's company, so that each prefers going to their dispreferred entertainment with their partner to going to their preferred entertainment alone.

Cultural stereotypes aside, this venerable example lays bare the essence of a coordination problem. The players in the game would prefer to coordinate their actions on some one of two (or more) possibilities but they disagree over which of these possibilities ought to be the one on which they coordinate. There is thus an admixture of common and divergent interests, and the possibility of both successful coordination (to the relative advantage of one or more of the players over the others) and failed coordination (to the disadvantage of all).