The appointment of a gay bishop in the US has put the Archbishop of Canterbury and the world's Anglican churches - the Anglican Communion - back in the spotlight.
What is the Anglican Communion?
A loose international network of separate, individual churches. They range from the liberal (the Episcopal Church in the US) to the more conservative (the Church of Nigeria).
There are nearly 70m people classed as "members" of 38 self-governing churches made up of about 500 dioceses, 30,000 parishes and 64,000 individual congregations in a total of 164 countries.
Who leads the Anglican Communion?
The Church of England's Archbishop of Canterbury, currently Dr Rowan Williams, is head of the Anglican Communion but in fact he has few formal powers.
He is responsible for inviting bishops from around the world to the Lambeth Conference. Every ten years the Conference debates and produces resolutions. But the resolutions are not binding on the churches - they reflect the 'mind of the bishops'.
Every year, the Archbishop also summons the leaders of each Anglican Church to the Primates Meeting, where they discuss recent developments.
But again, nothing binding comes out of the meetings. He certainly cannot force them to do anything. In fact, the Archbishop's main power is the moral authority of his office.
Can the current tensions within the Anglican Communion be resolved?
Here the Archbishop of Canterbury's moral authority can be particularly important. As primus inter pares (first among equals), he can urge patience, prayerfulness and, ultimately, compromise.
It remains to be seen how far this authority will influence the more than 40 churches within the Anglican Communion.
But for all the threats, breaking the spiritual link with the Church of England, and with Canterbury Cathedral, would be a major step for any church.
What about the Church of England?
The Archbishop of Canterbury's position in the Church of England is stronger: he is the President of the Archbishop's Council and Joint President of the General Synod, the Church's parliament.
But even these positions do not give him many formal powers.
The Church is 'hedged about with safeguards' and his only real powers are in Canterbury.
Again, most of his ability to influence others derives from the moral and spiritual authority of his office, and that authority looks likely to be sorely tested in the coming weeks.