An adequate understanding of the contemporary significance of religious freedom requires a grasp of its history and institutionalization over time. While the idea of religious freedom grows out of the Classical and Judeo-Christian traditions, it became a major social and political issue during and after the Reformation. Over the past two centuries, the idea of religious liberty has advanced against fierce opposition, both religious and secular, and has found diverse forms of political expression. Understanding the persistence of discrimination against and persecution of religious communities in the contemporary world—and countering it effectively—requires a deeper understanding of history. From 2011 to 2014 the Religious Freedom Project brought together leading scholars to examine the evolution of the idea of religious liberty, its institutionalization, and contemporary relevance.