Through extensive archival research in Poland, Germany, and the Netherlands, Klassen unearths rich material that has rarely, if ever, been studied previously. He demonstrates how the interaction of religious, political, and economic factors created a situation in Poland and Prussia that permitted a diversity of religious beliefs and practices.

Mennonites in Early Modern Poland and Prussia focuses on the large Mennonite community in these countries. Klassen reveals how the Anabaptist groups were treated and explores whether the uncommon religious freedom they enjoyed gave rise to a flourishing of their faith or a falling away from its central tenets.

Early modern Poland and Prussia are virtually ignored in most studies of the Reformation. Klassen brings them to light and life by focusing on an unusual oasis of tolerance in the midst of a Europe convulsed by the wars of religion.