The heads of state are expected to register GUAM as an international group and formally change its name to the Organization for Democracy and Economic Development.
They are also due to discuss deeper cooperation in the energy sphere, and ways to diversify energy sources. The region's "frozen conflicts" are also likely to be discussed.
In an interview with RFE/RL's Georgian Service, Georgian President Mikheil Saakashvili said the summit shows GUAM members are united.
"We should become stronger in all areas, both economically and politically," Saakashvili said. "We will be respected only when we are strong. But if we are weak, we will always have problems."
A number of officials from nonmember states are expected to attend the summit, including Polish President Lech Kaczynski, Lithuanian President Valdus Adamkus and Organization for Security and Cooperation in Europe (OSCE) Secretary-General Marc Perrin de Brichambaut.
Officials held low-level talks on the first day of the summit on May 22.
GUAM was founded in 1997 with the purpose of countering Russia's influence in the region. Uzbekistan became a member in 1999, but withdrew in 2005.