One of her first tasks will be appointing a new cabinet – it's expected she'll increase the number of women in top government positions when she succeeds David Cameron later.
And there's plenty of speculation about who'll get the job of the head of the Department of Finance.
British Foreign Secretary Philip Hammond is the favourite to take over from George Osborne.
Meanwhile former shadow cabinet member Owen Smith will announce his intention to stand for the Labour leadership later.
He'll join Angela Eagle in challenging Jeremy Corbyn.
