Trial by jury is one of the most controversial yet enduring modes of dispute resolution that the world has ever known. Over the centuries juries have been praised, parodied, and pilloried. The institution of jury trial seems under constant threat—from intellectual ideologues, from crass dictators, and from cost-cutting bureaucrats who see it as an expensive anachronism in a modern world. Some states that once made use of juries discarded them, only, like Russia and Spain, to reintroduce them later.

At the beginning of the twenty-first century, jury trial existed in some form in over fifty countries. It would be a daunting exercise to analyze each and every one of these systems, as the variations among them are many. Indeed, given the myriad of variations, identifying the core of what constitutes a jury is itself a challenge. In some countries, in particular the United States, juries decide both...