After a special service at Westminster Abbey later, the Queen is to open the Church of England's General Synod.
The synod gets the honour of a royal inauguration because this is the established, state church and the Queen is its supreme governor.
The synod - the Church's legislative body - is the only institution outside parliament that can make laws, even if it does have to get its decisions approved by a special parliamentary committee.
One of the most important laws likely to emerge in the synod's five-year term starting on Tuesday is the introduction of women bishops.
It has already been a debate that has deeply divided traditionalists from progressives, and led some on the Catholic wing of the Church to say they will take up the Pope's offer of a place in the Roman Catholic Church.
To many outside the Church - and to some Anglicans as well - so much anguish and dispute over what they regard as a logical progression from the ordination of women priests 16 years ago is unaccountable.
But for traditionalists - from both Anglo-Catholic and Protestant backgrounds - there is something fundamental at stake. Read more