In the years following Henry VIII’s separation from the Catholic Church and the formation of the Church of England, the king and his trusted religious advisor, Thomas Cranmer, Archbishop of Canterbury, led a divided church. A Necessary Doctrine, or The King’s Book, exemplifies the ongoing struggle in the Church of England between conservatives wanting to maintain some connection with Rome, and the reformers. A Necessary Doctrine, published in 1543, is a more conservative revision of the 1537 Bishop’s Book, which is itself an expansion on Cranmer’s first guidelines for the Church of England, The Ten Articles. This comprehensive work, written for the purpose of unifying the church and instructing its members in Christian doctrine, was the defining doctrine for the church until almost a decade later, when Cranmer published the Forty-Two Articles, under the reign of Edward VI. It remains a foundational work of the Church of England and a valuable resource for understanding this Church’s early history.