Q: What is the Commonwealth?
A: The Commonwealth is a voluntary association of 53 member countries - almost all of which were formerly under British rule.
It is made up of 2.4 billion people. Gambia has just rejoined the Commonwealth after a five-year absence.
-- The Commonwealth (@commonwealthsec) February 8, 2018
Q: When was it founded?
A: The modern Commonwealth was established by the London Declaration of 1949, just two years after India and Pakistan were granted independence, and when George VI was king.
Q: What does it do?
A: Leaders of the Commonwealth meet every two years at the Commonwealth Heads of Government Meeting (CHOGM), where they discuss issues of mutual concern and agree on collective policies and initiatives.
The 2018 CHOGM is being hosted in London and Windsor next month.
The Commonwealth follows a Charter, which outlines its joint values and aspirations - democracy, human rights and the rule of law.
-- The Commonwealth (@commonwealthsec) February 11, 2018
Q: And the Commonwealth Games?
A: The Commonwealth Games international multi-sport competition takes place every four years and involves athletes from Commonwealth countries.
This year's Games are being held on Australia's Gold Coast in April.
Q: What has the Commonwealth got to do with the Queen?
A: The Queen is head of the Commonwealth - a symbolic role.
She is also Queen of 16 of the 53 Commonwealth member countries, including the UK.
She holds no formal powers over the Commonwealth, but takes her role seriously and views the Commonwealth as a "family" and takes great pride in its success.
The Queen has been Head of the Commonwealth throughout her 65 year reign and as Head, Her Majesty personally reinforces the links by which the Commonwealth joins people together from around the world. https://t.co/pedxuxYRTf#CHOGM2018pic.twitter.com/ADvhka6gHn
-- The Royal Family (@RoyalFamily) February 1, 2018
Q: Why is succession an issue?
A: Although the Queen took over from her father George VI, the post is not a hereditary position.
It will not automatically pass on to the Prince of Wales when he becomes king, but it will be up to the leaders of member states to decide what to do with the role.
Q: How is the Prince of Wales involved in the Commonwealth?
A: Heir to the throne Charles's involvement in CHOGM events has stepped up in recent years.
He formally opened the summit in Sri Lanka in 2013, representing his mother in the role for the first time - a significant move for him as a king-in-waiting.
The then-Commonwealth secretary-general, Kamalesh Sharma, spoke of how Charles's support for the Commonwealth had "deepened" its connections to the Crown, prompting speculation the prince could eventually inherit the Head of the Commonwealth post.
Q: What has the prince said about the Commonwealth?
A: Charles has recently spoken passionately about its role.
In a speech in Singapore in October, he described how much the Commonwealth meant to him personally, saying it had been a "cornerstone" of his life.
In Malaysia, he also stressed that the Commonwealth can play a "pivotal" role in tackling global challenges, drawing on its "wide range of national contexts, experiences, traditions".