The Pope addressed thousands of Catholics in Washington as he led his first mass in the United States.
The Pope is celebrating Mass outside the Basilica of the National Shrine of the Immaculate Conception.
During the service he will elevate an 18th-century Franciscan friar to sainthood, in a first canonisation in the United States.
More than 2,000 men and women studying to be Catholic priests and nuns were invited from around the country to attend.
Pope Francis has arrived to give his first mass in the United States.
The Pope, who is on a five-day visit to the country, is addressing Catholics outside the Basilica of the National Shrine of the Immaculate Conception.
During the long walk through the basilica, Francis waved as he was greeted by hundreds of well-wishers.
Pope Francis used his address at the White House to call for action to combat climate change.
Speaking in front of a crowd of thousands, the pope called climate change a problem that "can no longer be left to a future generation".
The Pope delivered a strong message against those who doubt the science of climate change, saying that the warming planet "demands on our part a serious and responsible recognition" of conditions awaiting today's children.
The pope also called to protect religious liberties - "one of America's most precious possessions".
The Pope also spoke privately with President Obama for about half an hour.
President Obama has welcomed Pope Francis to the United States.
Mr Obama said "the size and spirit of today’s gathering is just a small reflection of the deep devotion of some 70 million American Catholics".
Mr Obama spoke about the scripture’s call to “lift up the poor and the marginalized, to stand up for justice and against inequality.”
You remind us that “the Lord’s most powerful message” is mercy. That means welcoming the stranger with empathy and a truly open heart – from the refugee who flees war torn lands, to the immigrant who leaves home in search of a better life. It means showing compassion and love for the marginalized and the outcast, those who have suffered, and those who seek redemption.
Pope Francis begins his six day tour of the US.
ITV News Correspondent Robert Moore was there to see him arrive in a Fiat 500.
Crowds cheered as he whizzed past in a humble Fiat 500 before reaching his residence in Washington.
In the Pope's first trip to the US he will visit the White House on Wednesday and address Congress on Thursday.
He will meet lawmakers and politicians, but also prisoners, labourers and immigrants.
The Pope arrived to cheering crowds at his residence in Washington in a Fiat car.
He decided against the safety and comfort of bulletproof limousines that most world leaders usually opt for and travelled in a humble Fiat.
It is the Pope's first trip to the US. He is planning to visit the White House on Wednesday and address Congress on Thursday.
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Pope Francis has described life imprisonment as being like a "hidden death penalty" as he began his first visit to the United States.
Ahead of becoming the first pope to address Congress on Thursday, he remained tight-lipped on the contents of the speech, amid much speculation about what he might say about the US trade embargo on Cuba.
Speaking to reporters on his flight from Cuba, he expressed distress at long prison sentences, saying: "Life imprisonment is almost a hidden death penalty. You are there and you are dying every day without any hope of freedom."
On the subject of his speech, he said it would address "bi-lateral relations and multi-national relations as a sign of progress and coexistence".
Discussing US relations with Cuba, he said: "My desire is that they end up with a good result, that they reach an accord that satisfies both sides, an accord, certainly."
On Friday, the US announced new rules that further eased trade with the Communist-run island.