The Catholic Church extended its authority over many areas of life in the Later Middle Ages, and this increasingly led it into political conflicts with kings and other rulers. In this book, Peter Clarke focuses on one of the Church's chief weapons in these struggles - the interdict. A sanction that could be imposed on an entire kingdom, an interdict was similar to a strike in which clergy closed churches and refused to perform most religious ministrations. It was therefore a major event in medieval society, and this book is the first in-depth treatment of this phenomenon, exploring the issues of collective guilt and responsibility that are still important today.