Among the world leaders gathering this week at the United Nations to tackle problems ranging from climate change to the spread of nuclear weapons will be many new faces, including the presidents of the United States, Russia and China.
Libyan leader Moammar Gadhafi will also be making his first UN appearance after 40 years as ruler of the oil-rich north African nation, an appearance which has generated widespread interest and controversy.
Demonstrators have announced protests against Gadhafi over Scotland's controversial recent release of Libyan Abdel Baset al-Megrahi, the only person convicted of the 1988 bombing of Pan Am Flight 103 which killed 259 people, mainly Americans.
Iranian President Mahmoud Ahmadinejad, a veteran of UN General Assembly meetings, will also be the target of demonstrators protesting the recent disputed election which gave him a second term as well as his anti-Israeli views and questioning of the Holocaust.
More than 120 presidents and prime ministers and dozens of foreign ministers will attend the General Assembly's annual ministerial meeting, which runs through Sept. 28. They include the leaders of the five nuclear powers who are permanent Security Council members - President Barack Obama, Russian President Dmitry Medvedev, Chinese President Hu Jintao, French President Nicolas Sarkozy and British Prime Minister Gordon Brown.
Secretary-General Ban Ki-moon invited leaders to come to New York a day before Wednesday's opening of the UN General Assembly's annual ministerial meeting for a climate summit to generate political momentum ahead of crucial talks in Copenhagen in December on a new treaty to curb global warming.
The fact that over 100 leaders will attend Tuesday's summit - the largest number ever to discuss climate change - shows that they realize "this is an issue of great urgency ... requiring global partnership," Ban told a news conference Thursday.
This will be Obama's debut on the world stage, and diplomats say he is likely to get a standing ovation after his General Assembly speech because of the shift in the US tone to global engagement and his outreach to the Muslim world.
US Ambassador Susan Rice said Obama will deliver the message that cooperation and leadership from a wide range of countries is needed to face the "pressing array of global challenges" from terrorism, genocide, mass atrocities and cyber attacks to nuclear activities in Iran and North Korea, pandemic diseases and international criminal networks.
"In the 21st century, America's security and well-being is in fact inextricably linked to the security and well-being of people elsewhere," Rice told a White House briefing on Friday. "And the United Nations is thus essential to our efforts to galvanize concerted international action to make Americans safer and more secure."
Obama will chair a high-level meeting of the UN Security Council Thursday on disarmament and efforts to halt the spread of nuclear weapons.
Rice said the session will underscore the global reach of proliferation threats and steps to reduce nuclear dangers.
The council is expected to adopt a resolution focusing on these broad issues. Though it won't name any countries, the draft resolution does refer to previous council resolutions that imposed sanctions on Iran and North Korea for their nuclear pursuits.
Foreign ministers from the five permanent council nations and Germany, who have been trying to curb Iran's nuclear ambitions, will meet with the European Union's top negotiator on Wednesday to discuss prospects and expectations for lower-level talks with Iranian officials on Oct. 1.
In UN corridors, there has been much speculation on whether Obama and Ahmadinejad will meet and shake hands.
They are both invited to the secretary-general's lunch Wednesday following the opening of the ministerial session - and they are both expected to be part of the annual group photo of all participants.
Gadhafi and Obama are almost certain to meet because the Libyan leader addresses the General Assembly immediately after the US president on Wednesday. Libya is also a non-permanent member of the Security Council and Gadhafi is expected to participate in Thursday's meeting on disarmament and nonproliferation.
Obama plans to bring two opponents together: Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas. They will meet the US leader on Tuesday for what will be the first Israeli-Palestinian meeting since Netanyahu took office in March.
However, the Israeli and Palestinian leaders remain far apart on what it takes to resume peace talks that broke off in 2008, under Netanyahu's predecessor, and it appears unlikely Tuesday's trilateral meeting would restart negotiations.
Obama hopes he can resolve a showdown over Israeli settlement construction and get the sides talking again after months of deadlock.
There are many other meetings scheduled on the sidelines of the General Assembly.
Countries concerned with Myanmar, Pakistan and Afghanistan will hold closed-door talks. There will be commemorations of the 60th anniversary of the UN agency that deals with Palestinian refugees and of the Geneva Conventions. And there will be a two-day meeting to press for ratification of the nuclear test ban treaty, to name a few.
The General Assembly is taking place a year after the global economic crisis began and Ban expressed concern that despite reports of "green shoots of recovery" UN data show that over 100 million more people are expected to fall below the poverty line this year - with those who escaped poverty over the last decade becoming "the new poor."
The secretary-general and leaders of the 20 major economies will fly to Pittsburgh, Pennsylvania on Thursday for a summit of the G-20 which will focus on ways to promote a global economic recovery and prevent another financial crisis.