This article focuses on a very important issue in the relationship between Church and State in Early Modern England: the scope of the monarch's power over the Church, or, the royal supremacy. It investigates the presentation of the issue in The Life and Raigne of King Henry VIII by Edward, Herbert of Cherbury (1582-1648). The first section examines the development of the royal supremacy from the Tudors to the Early Stuarts and the moral dilemmas it brought to the people. Moral dilemmas emerged especially when the individual's conscience disagreed with the religious opinions of the monarch and the regulations of the Church. The second section examines the viewpoints of five authors who wrote the history of King Henry VIII, and reveals that Herbert's work had for a long been controversial and its value underestimated. Then the following three sections examine several issues related to the royal supremacy in The Life and Raigne, including the controversy between the Pope and the King, the crown's spiritual powers in the Church, and the martyrs who infringed the laws of the supremacy. The findings are two-fold: (1) Herbert agreed with the mainstream opinion in Early Modern England that the monarch's powers over the Church were jurisdictional rather than sacerdotal. However, he used an unusual way to justify his arguments by applying his philosophical theory to issues related to the royal supremacy. (2) Herbert only offered limited support for the royal supremacy and believed that it should not encroach upon the judgement of individual conscience. Conscience, in Herbert's view, marks the limit of the king's power over the Church, which was a major concern in the seventeenth century.