The Friday meeting between President Obama and the pontiff does not fit the standard in traditional Vatican protocol.
The Holy See clearly wanted the meeting, arranging an unorthodox late afternoon gathering and live televised coverage to accommodate Mr. Obama's schedule in Italy.
In advance of their meeting, the White House said it expected "frank" and constructive talks between the president and Pope Benedict XVI.
The two men share a deep concern for helping the poor, as evidenced with the President's announcement that G8 leaders had pledged $20 billion to combat world hunger. Obama called it a moral obligation of wealthy nations to fight poverty and hunger around the world.
The two men also are committed to seeing peace in the Middle East. During the pope's tour through the region earlier this year, he called for a Palestinian state to coexist beside Israel.
The Vatican sees a potential White House ally on both of these matters.
The two leaders disagree are on issues regarding the sanctity of life, such as abortion and stem cell research.
A fire-storm brewed among pro-life Catholics when Obama delivered the commencement address at Notre Dame in May.
The Vatican instead decided to focus on Obama's message of finding common ground and reducing abortions.
The pontiff realizes they may not see eye-to-eye on everything, but the Vatican saw a close ally with former President Bush on life issues, even though it opposed the Iraq war.