King John is a study of a king and of his time. The early thirteenth century was a period of profound social and political change, and of unprecedented insecurity. Warren explores the king's personality so distorted by the accounts of such chroniclers as Roger of Wendover and Matthew Paris, through his achievements and his failures, but considers him also against the background of his predecessors, of the society in which he lived and of problems independent of his making.

The result is a fair-minded, revealing and readable account which analyses the disputed succession, the conflict with France, the clash with Pope Innocent III, and the events leading to Magna Carta. Warren is unsparing in his criticism of King John's failings, but acknowledges the decisive impact of his remarkable personal qualities. A new foreword written for this edition by D. A. Carpenter assesses Warren's achievement in the light of recent scholarship.