Prime Minister David Cameron:
"It's absolutely wonderful news, and I'm delighted for them and I'm sure they will make absolutely brilliant parents. I'm sure people round the country will be celebrating with them tonight. A little note came into a meeting I was having and I found it quite difficult to keep it to myself."
First Minister Alex Salmond: "My warmest congratulations and sincere best wishes to the Earl and Countess of Strathearn on this wonderful news. Everyone in Scotland will join me in wishing the couple the very best as they prepare for the birth of their first child."
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The Archbishop of Canterbury Dr Rowan Williams, who married the couple in Westminster Abbey in April 2011: "The whole nation will want to join in celebrating this wonderful news. We wish the Duchess the best of health and happiness in the months ahead."
A spokesman for President Obama: "On behalf of everyone here - beginning with the President and First Lady, we extend our congratulations to the Duke and Duchess of Cambridge on the welcome news we received from London that they are expecting their first child."
A spokeswoman for the University of St Andrews, where the couple studied: "We are delighted for the couple and will be writing to them to offer our congratulations."
A spokesman for the RAF, with which William serves: "The RAF is delighted with the news and wishes the Duke and Duchess of Cambridge all the best for the future."