This introduction provides an overview of the key concepts discussed in the subsequent chapters of this book. The book compares the modern development, organization, and practice of constitutional and statutory schemes of clemency and pardon throughout the common law world. Most of the world's legal systems have a provision for mercy in criminal cases to temper the overly harsh application of law without undermining the law's common law world. Although it plays a small role in modern criminal law, the pardon looms large in historical memory as evidenced by the quest for posthumous pardons, especially in cases with overt political overtones such as sympathetic rebellious leaders or wrongfully convicted political prisoners. Main reason for the decline of the pardon power is the global decline of the death penalty. Judeo-Christian traditions emphasize the personal virtues of forgiveness and compassion, with followers placing their faith in the mercifulness of God's justice and the justice of God's mercy.