Neither of these answers reflects the more important historical roots of the English Reformation, a desire for independence from the Roman Papacy, which, due to the political activities of the Papal States, was actually a (moderately hostile) temporal foreign power as well as an ecclesiastical one, allied with England's enemies. This distrust of the Papacy, and reluctance to have a foreign Pope appoint Bishops who sat in the House of Lords and have control of huge tracts of land in England, dates back as far as the Acts of Praemunire, Provisions, and Provisors in the fourteenth century.
One of the great tensions in the institutional structure of Christianity from its origins had been the centripetal force, impelled by the needs of the Roman emperors who made Christianity a state religion, to have Christianity unified with a coherent bureaucracy and power structure, versus the centrifugal tendencies towards regional or even congregational independence. The notion that the Bishop of Rome should proclaim himself a "Pope", overriding ecumenical councils unilaterally (by, for example, adding the "filioque" to the Nicene Creed), and claiming dominance over other archbishops such as the Patriarch of Constantinople, was never something uniformly accepted by all Christians; in some ways, the organizational structure of the Church of England could be considered as reclaiming many of the Orthodox traditions of episcopal structure (which have continued from early Christianity to the present day) from which the Roman Catholic Church had departed.
There were also many proto-Protestant movements in England before the establishment of the Church of England including the Lollards, who, contra the above post, were generally poor and uneducated, and not members of the noble elites. Although the events of Henry VIII's life were certainly the catalyst for the final step of a break with Rome, the tensions leading up to the break had existed ever since the introduction of Christianity in England. While the 664 Synod of Whitby imposed a Roman model of Christianity on England, this imposition was controversial and far from uniformly popular. To account for the English reformation simply in terms of the events of a few years is to drastically oversimplify issues that had a long and complex history.
I respectfully disagree with the above post. The English Reformation was the result of Henry VIII's desire to obtain a divorce from Catherine of Aragon, pure and simple. There was no basis in philosophy, thought, or politics that brought it about.
Henry had only ascended the throne after the premature death of his brother Arthur who was first married to Catherine. The marriage had been a political one to preserve an alliance with Spain. Henry's father, Henry VII, had then arranged for the younger Henry to marry Catherine to preserve the alliance. There was a Biblical problem, as it was considered a sin for a man to marry his brother's wife. Henry quickly secured a dispensation from the Pope based on the heavy presumption that the marriage between Arthur and Catherine had not been consummated; a requirement for a true "marriage."
Henry desperately needed a male heir, but Catherine had only one surviving child, the future Mary 1. Several sons were stillborn. Because Catherine was fast moving past child bearing age, Henry, either through conviction but probably through desperation, decided that the marriage between Catherine and Arthur had in fact been consummated, and his marriage was a sin. He then asked for the marriage to be annulled by the Pope, which Catherine resisted. In the essence of poor timing, Catherine's nephew, the Holy Roman Emperor Charles V had captured Rome and held the Pope hostage. The Pope did not dare annul the marriage and insult his jailer. Again, probably from desperation and through the auspices of his Chancellor, Thomas Cromwell, Henry had Parliament pass the Act of Supremacy which declared the king to be head of the Church in England and severed any relationship with Rome. He then managed to secure a divorce from Catherine and married his mistress, Anne Boleyn who as already pregnant. (Ironically, Anne produced only a female heir, the future Elizabeth I. She too had sons stillborn.) Later, to fund his wars and other efforts, Henry closed the English Catholic monasteries and seized their wealth. This action forever precluded a return to Roman Catholicism. So high sounding motives aside, it was simply Henry's desire to obtain a male heir that caused the English Reformation, nothing more. The link below provides more specific information.
There were many causes of the English Reformation. Some of them were common to both the English Reformation and the broader Protestant Reformation while others were unique to England.
In general, the Reformations in England and elsewhere were made possible by changes in technology and in ways of thinking. The new, more scientific mindset of the time encouraged people to think for themselves instead of accepting the received wisdom of the authorities. The printing press allowed the circulation of reformist ideas among the people and, perhaps more importantly, made it possible for relatively many people to own Bibles. All of these things made the Reformation more possible.
In England, there were many political causes of the Reformation and the Reformation was driven more by the needs of leaders than by the demands of the people. Most importantly, the desire of Henry VIII for more power in England was a major driver of the English Reformation. Henry's desire to control the Church in England (along with his famous desire to divorce Catherine of Aragon) led him to support reforms that would eventually abolish the Catholic Church in England and replace it with the Church of England, which was subordinated to the Crown.