PHOTOS: Keep Up with the Pope's Trip to Cuba and the United States

Pope Francis greeted a crowd outside the Cathedral Basilica of Saints Peter and Paul on Saturday in Philadelphia before giving a mass about religious tolerance.

The pontiff cracked a smile during the mass in Philadelphia.

Many gathered at the cathedral to hear the pope's homily on Saturday, including many important members of the Catholic church.

The pontiff mad his way through the crowd as he traveled to the Festival of Families in Philadelphia.

On Friday night, the pope celebrated mass at Madison Square Garden in New York City, which was his final night in the Big Apple.

Friday afternoon was Pope Francis' most adorable appointment of the day: Meeting Catholic school students at Our Lady Queen of Angels in Harlem with Cardinal Dolan. Once the school bells ring, the Pope will set off in a motorcade through Central Park to greet New Yorkers before closing out the New York City leg of his trip with evening mass at Madison Square Garden.

Outside of Our Lady Queen of Angels School in Harlem, he stopped to take a few photos with the crowd that had gathered to greet him.

After a morning spent at the United Nations, the pope headed downtown to the World Trade Center to visit the National September 11 Memorial and Museum.

There, the pontiff took some time to pray for all those who lost their lives in in the Sept. 11, 2011, terrorist attacks …

… and paid tribute to the victims by placing flowers on the memorial after he finished praying.

After paying his respects, the Pope headed inside, where he led an interfaith prayer service for peace.

Naturally, the pontiff was greeted by crowds of people, some of whom had been waiting there for hours.

Pope Francis was joined on the stage by religious leaders representing faiths including Islam, Judaism, Christianity, Hinduism and Sikhism.

During the service, a very emotional pope spoke out against religious fanaticism, and encouraged the other religious leaders present to join him in being a force for peace and justice.

He also offered a prayer that had originally been offered by Pope Benedict XVI, who visited the World Trade Center in 2008, before the memorial was completed.

Many of the other leaders present offered their own prayers of peace, and like, Pope Francis – who delivered his address in Spanish – they spoke in their native tongues.

After the service, the pope was treated to a tour of the museum by former New York City Mayor Michael Bloomberg.

The pair was joined by the press for their trip through the exhibition hall.

Things were a bit calmer when Pope Francis also took in the Ladder Company 3 truck alongside the current Archbishop of New York, Cardinal Timothy Dolan.

Pope Francis stopped to shake the hand of a New York Police Department officer outside in the Memorial Plaza.

Bloomberg wasn't the only Mayor present on Friday – the pontiff also made time to meet with the current Mayor of New York, Bill de Blasio, and his wife, Chirlane McCray.

Pope Francis headed out bright and early Friday morning for a visit to the United Nations, where he brightened up staff members' mornings by greeting them with Secretary General Ban Ki-moon.

On his way to the podium to address the U.N. General Assembly, the pontiff was greeted with a standing ovation.

During his speech – which kicked off a meeting of the U.N. Sustainable Development Summit – Pope Francis urged world leaders to work harder to combat global warming.

Nearly 48 hours after arriving, Pope Francis was back at Joint Base Andrews in Maryland, boarding a flight from Washington, D.C., to New York City.

While in D.C., Pope Francis visited the Catholic Charities of the Archdiocese of Washington, where he was greeted by locals …

… and even took a few selfies with them! Talk about a modern pope.

Back at the Vatican Embassy in Washington, D.C., Pope Francis kissed the cheek of a girl waiting in the crowd.

On his final day in Washington, D.C., crowds swarmed as Pope Francis arrived at St. Patrick's Church.

Well-wishers at St. Patrick's grabbed Francis' hand.

This little girl may not remember being blessed by Pope Francis – but judging by her tearful look, her mom sure will!

A highlight of the pope's time in Washington, D.C., was his congressional address. Here, he arrives at the joint meeting of Congress in the Capitol while Secretary of State John Kerry looks on.

Before speaking to Congress, Pope Francis met with the Speaker of the House, John Boehner, on Capitol Hill.

Standing before a joint meeting of Congress, Pope Francis turned to greet Vice President Joe Biden and Speaker of the House Boehner.

During his address, the pope discussed the importance of taking action against climate change and working to improve the lives of those living in poverty.

Pope Francis made history with his speech, becoming the first ever pontiff to address Congress.

After addressing Congress, Pope Francis greeted the crowd waiting outside the Capitol. The pontiff brought crowds out to the National Mall that rivaled the size of a presidential inauguration.

To end his first full day in D.C. on Wednesday, Pope Francis visited the Basilica of the National Shrine of the Immaculate Conception.

He entered the Basilica, led in by a number of bishops.

While he was there, he performed Mass and also canonized the first saint on U.S. soil. Junipero Serra, a friar who founded a mission in Baja California back in the 1700s, was canonized during the Mass.

The pope is a pretty popular guy: seminarians greeted Francis – and clamored for pictures of him – as he entered the basilica.

Security is tight for the pope's visit – but Francis had nothing but kindness for this little girl, who broke protocol to meet the pontiff face-to-face in Washington, D.C., on Wednesday.

At the Apostolic Nunciature, a Vatican mission where Pope Francis is staying during his time in the U.S. capital city, the pope greeted a woman in a wheelchair at the front of the crowd.

At the Cathedral of St. Matthew, Pope Francis stood at the podium to address a group of bishops during the midday prayer service.

During the service, a bishop bowed his head toward the pontiff.

Earlier, at the White House, the pope spoke in favor of the U.S. reestablishing a relationship with Cuba as well as taking action against climate change.

The pope spent the early afternoon at the Cathedral following his meeting with President Obama at the White House that morning.

The pope and his D.C. hosts, President Obama and First Lady Michelle Obama, waved to people from a White House balcony on Wednesday.

Crowds gathered on the South Lawn of the White House on Wednesday for the pope's official state arrival ceremony.

Pope Francis and President Obama stood still as the National Anthem was played during the pope's official welcoming ceremony.

A must-do for any visiting dignitary? A trip the Oval Office! Pope Francis checked it off his bucket list on Wednesday morning.

It wasn't all just business they discussed – although later on Pope Francis gave a serious speech on religious liberty and climate change, the president and pope laughed together in the Oval Office.

Outside the Apostolic Nunciature, the Vatican's diplomatic mission in Washington, where Pope Francis is staying while in D.C., hoards of people waited to catch a glimpse of – or a selfie with – the pontiff.

The crowds came with signs, too, including a banner that conveyed the city's sentiment toward the pontiff clearly: "We Love the Pope."

This man, who kissed Francis on the head, got a bit more than just a glance of his holiness!

He's here! After his four days in Cuba, Pope Francis arrived in the United States on Tuesday for the first stop on his visit: Washington, D.C. This marks the first time he's ever made a trip to the United Sates as pontiff.

Walking down from his chartered Italian jet, the pope was met with choruses of "Welcome to the U.S.A.! Ho ho! Hey hey!"

Pope Francis had quite the welcoming committee stateside: President Obama, First Lady Michelle Obama, daughters Malia and Sasha Obama, as well as Vice President Joe Biden.

Soon after arriving in Washington, Pope Francis had a brief, private meeting with President Obama.

The popemobile of choice in Washington, D.C.? A Fiat 500L, which he drove off in after arriving at Andrews Air Force Base in Maryland.

His visit to the United States will really kick off on Wednesday, with a welcome ceremony at the White House.

Later on, Pope Francis will conduct the first-ever canonization on U.S. soil at the Basilica of the National Shrine of the Immaculate Conception.

Before landing in the U.S., Pope Francis spent four days in Cuba. To mark his first full day in the nation, Pope Francis held a mass at the Plaza of the Revolution in Havana on Sunday.

Hundreds of thousands of people came out to the Plaza de la Revolucién to watch the pope hold mass.

The second day of Francis' Cuba visit was a big one: He met with former Cuban President Fidel Castro and his wife, Dalia Soto del Valle, in Havana on Sunday.

While in Cuba, the pope visited a Havana Jesuit community, where he met with children and families on Monday.

On his last day in Cuba, Pope Francis addressed the crowd gathered at the Cathedral of Our Lady of the Assumption in Santiago de Cuba.

Afterward, Pope Francis greeted a baby following a mass and blessing at the Santiago de Cuba cathedral.

And he's off! Pope Francis boards a flight from Rome, Italy, to Havana, Cuba, on Saturday, kicking off his tour of the island nation and later, the United States. The visit marks his longest papal trip, and also his first time to the States.

Upgrades for Pope Francis included painting Reina Street, a main thoroughfare in Havana on which he'll ride in the Popemobile. The 78-year-old is only the third Pope to visit Cuba.

In this shot, locals prep flowers they'll sell near the Pope's route from the airport to the papal ambassador's home.

Flags of Cuba (left) and the Vatican hang on a balcony on Reina Street on Saturday. During his stay in the Caribbean island, the Pope will host mass in the famous Plaza de la Revolucién on Sunday morning, and then will meet with President Raul Castro. He is also expected to meet with former leader Fidel Castro, according to TIME.

Francis met with President Raul Castro during an arrival ceremony at the airport in Havana. During the reception, both Castro and the pope gave speeches, with the latter saying conversations between Cuba and the United States is "a sign of the victory of the culture of encounter and dialogue."

After the airport reception, Francis rode through to streets to Apostolic Nunciature, where he will be residing during his stay. The pontiff was greeted by thousands of well-wishers, who chanted "we want a gift," as he made his way through the streets. Traditionally, Cuba's government has granted Christian holidays after a papal visits. The communist country already recognizes Christmas Day and Easter and many Catholics are hoping for another holiday.

Whoops! Will deplaning in Havana, Francis' papal cap flew off with a gust of wind. The pope smiled and continued on his path while a security team member retrieved the runaway hat.

Francis made his way from his plane to a podium where he would be formally welcomed to Cuba.

On Sunday, the pope gave his first mass in Cuba, where he preached about having love for one another, according to TIME. "All of us are called by virtue of our Christian vocation to that service which truly serves, and to help one another not to be tempted by a 'service' which is really 'self-serving,'" he said. "All of us are asked, indeed urged, by Jesus to care for one another out of love. ... Jesus tells us: Whoever would be first among you must be the last, and the servant of all.' He does not say: if your neighbor wants to be first, let him be the servant!"