The alliance's mission in Afghanistan, where its troops are tackling a resurgent Taliban, is expected to top the agenda.
It is the first time a NATO summit has been held on the territory of the former Soviet Union.
On the eve of the summit, U.S. Foreign Relations Committee Chairman Richard Lugar (Republican, Indiana) warned that failure of member states to commit whole-heartedly to Afghanistan could deal a serious blow to NATO's credibility.
"If the most prominent alliance in modern history were to fail in its first operation outside of Europe due to a lack of will by its members, the efficacy of NATO and the ability to take joint action against a terrorist threat would be called into question," Lugar said.
NATO leaders are also expected to discuss the ongoing tensions between Russia and Georgia, and how to avert potential threats to energy supplies.
Lugar also said the same day that he is looking forward to "welcoming Georgia in NATO."
Speaking to journalists in Riga, Lugar said NATO should invite Georgia to join the alliance, though he did not say when he expected this to happen.
"Georgia has become a superb role model for the region and is host to critical segments of the Baku-Tbilisi-Ceyhan oil pipeline and the southern Caucasus natural gas pipeline," Lugar said. "Two months ago, the NATO secretary-general announced that the alliance had launched an intensified dialogue with Georgia. This is an important step, but NATO must [form] a Membership Action Plan as soon as possible in my judgment."
Earlier this month, the U.S. Senate passed legislation urging NATO to act quickly to accept Georgia, Albania, Croatia, and Macedonia as members.
Russia has expressed its "categorical" opposition to Georgia entering NATO.
(Reuters, AFP, AP, dpa)