The trip is Rule's first project as first lady of Chicago. On Thursday, she will offer an official Chicago welcome at NATO.
The delegation's goal is to spread goodwill and sell Chicago's place on the global stage.
The diverse city of Brussels is the threshold for much international diplomacy with the European Union and North Atlantic Treaty Organization headquartered there.
In coming weeks, preparing for the NATO summit in Chicago is critical to future moves by NATO allies.
"I think there is going to be an excitement building up in this building among the delegations about Chicago," said Ivo Daalder, U.S. Ambassador to NATO. "That is part of what we're trying to do, create excitement about Chicago so that when we get there, everyone is dedicated to make it a success."
In the 1960s, there was a formal inauguration of the Brussels headquarters. But NATO formed in 1949 in the aftermath of World War II and a growing Soviet threat. It was a defensive alliance initially but its role in the world has evolved with other threats, including the attacks of 9/11 that prompted NATO action in Afghanistan. That involvement and exiting Afghanistan by 2014 will be the allies' priority in Chicago.
"NATO and the United States and all the countries involved will continue to work with them and to provide an enduring presence in the country so that we never again are faced with what we were faced with on September 11," said Ambassador Daalder.
President Obama offered to host the NATO Summit in his home town, giving Chicagoans an up-close look at world events and opportunity to shine the light on Chicago to potential trade partners and foreign tourists.
"It is a great opportunity to come here to talk about the city, to showcase the city's attraction," said Lori Healey, NATO Summit Host Committee. "We say, come early, stay late, experience the best Chicago has to offer."
The summit agenda will emphasize our interconnectedness with the world -- from terrorists threats to gas prices -- and the importance of partnership, diplomacy and dialogue.
On Wednesday, there was a meeting encouraging Chicago tourism and on Thursday Gov. Quinn will meet with potential investors.