The Thirty Years' War (1618-1648) remains a puzzling and complex subject for students and scholars alike. This is hardly surprising since it is often contested among historians whether it is actually appropriate to speak of a single war or a series of conflicts. Similarly emphasis is also put on the different motives for going to war, as conflicting religious and political interests were involved. This research companion brings together leading scholars in the field to synthesize the range of existing research on the war, which is still fragmented and divided along national historical lines, and to further explore the complexities of the conflict using an innovative comparative approach. The companion is designed to provide scholars and graduate students with a comprehensive and authoritative overview of research on one of the most destructive conflicts in European history.