Religious non-conformity in England
In the 16th century, Henry VIII of England broke from the Catholic church to establish the Church of England, also known as the Anglican church. The motives for this action can be debated. Many believe that it was based solely on his desire to have his marriage annuled so that could marry another woman who he believed could give him an heir to the throne. Some believe it was an act of religious faith.
In any case, the new church (also called the Established Church) was not universally welcomed and quickly became politicized. Rejection of the Established Church became seen as a rejection of the Crown. Many who dared to challenge the Established Church were interested in remaining loyal to the Catholic (i.e., univeral) church headquartered in Rome. They became known as Roman Catholics. There were others who agreed with a separation from Rome, but had other ideas about the form such a "protest" should take. They were part of a larger Protestant movement sweeping through Europe around this time.
However, in England, these ideas were seen as political protest, not just religious protest. For this reason, English Protestants are often referred to as Dissenters or Non-conformists.
Throughout the late 1500s, many Roman Catholic and Non-conformist leaders were burned at the stake (some after death; others while still alive). Throughout most of the 1600s, Sunday attendance in the Established (Anglican) church was mandatory for all and those not attending could be fined and punished. Although the "Act of Toleration" introduced a degree of religious freedom in 1689, many still kept their association with non-conformist movements a secret, often being baptized in both the Protestant and the Anglican churches.
As the years passed, association with a Non-conformist church (such as Baptist, Presbyterian, or Methodist) became more accepted. Hardwicke's Marriage Act (1753) required marriage in an Anglican church, so that a non-conformist ancestor may show a baptism in a non-conformist church and a marriage in an establish parish belonging to the Church of England - suggesting (erroneously) a conversion. It wasn't until 1837 that a couple could be legally married in a non-Anglican parish church.
Some of this information came from Mark D. Herber, Ancestral Trails: The Complete Guide to British Genealogy and Family History (Baltimore, MD: Genealogical Publishing Co., 1998).