Of all the documents surviving from the Middle Ages, Magna Carta has a unique facination. In stolid legal Latin, some sixty-odd clauses regulate such interesting matters as the abolition of fish weirs on the Thames, rates of composition payments for military obligations, and standard weights and measures ("a broadcloth to be two ells wide within the selvedges"). But among many obsolete clauses is enshrined a principle so important that it is the very rock upon which democratic constitutions are founded: that government shall ultimately and effectively be accountable to the governed. The society which established this principle, the struggle which led to its formulation, the history of interpretations, misinterpretations and endorsements is the subject of this book.