The prime minister has described the Queen as one of the world's greatest-ever leaders, as she opened two days of tributes in Parliament.
Lis Truss, who was appointed PM by the monarch just three days ago, said she was an "icon" of modern Britain.
Her predecessor Boris Johnson told MPs "Elizabeth the Great" had taught the nation "how to give, how to love, and how to serve".
MPs held a minute's silence to mark her death after 70 years on the throne.
Both houses of Parliament will sit on Friday and Saturday to allow politicians to pay tribute to the Queen, following her death on Thursday.
Opening the tributes in a sombre House of Commons, Ms Truss said the Queen's "sheer humanity" had made her "loved and admired" all over the world.
Her reign, she added, had been "dignified but not distant," allowing her to re-invent the monarchy for the modern age.
Labour leader Sir Keir Starmer said the Queen had enjoyed a "personal relationship with us all," based on "total commitment" to duty and a "deep devotion to the country, the Commonwealth, and the people she loved."
"In return for that, we loved her. And it is because of that great, shared love that we grieve today," he added.