The Worldwide Anglican Communion
In today's world, The Anglican Church is taken to mean those tens of millions of people who worship in churches that are part of the Anglican Communion. Some churches whose name contains the word "Anglican" are part of the Anglican Communion and some are not. The Anglican Communion Office in London is its administrative headquarters, and that office has its own web page.
The Anglican Communion inherits many centuries of catholic and apostolic tradition, especially that part which began in the British Isles. Although Christian missionaries had reached England by the time of the Council of Jerusalem in 50 AD, the foundation of the Anglican Church is often described as having begun with the arrival in 597 AD of St. Augustine, first Archbishop of Canterbury.
When the Romans withdrew from Britain in 407 AD, they left a legacy of Christianity among the Celtic people. Those Celtic Christian churches were largely still in existence when Augustine arrived two centuries later, though they had become isolated from Rome. In particular, they survived in Wales, Ireland, and Scotland, and they helped to ensure that, from its beginnings, the Anglican Communion was not exclusively English in origin.
When the English people settled the British Empire they took their religion with them and thus the Church of England spread overseas. Eventually these overseas parishs became autonomous provinces of the Communion. These churches, while autonomous in their governance, are bound together by tradition, Scripture, and the inheritance they have received from the Church of England. They together make up the Anglican Communion, a body headed spiritually by the Archbishop of Canterbury.
If an Anglican church is a member of the Anglican Communion, it is said to be "in communion", or "in communion with the See of Canterbury". Otherwise it is said to be "not in communion." Generally, Anglican churches that are not in communion with the See of Canterbury have withdrawn because of doctrinal differences. In recent years those differences have included the ordination of women priests and the attitude of the church towards sexuality.