The goal is to protect the president, heads of state and diplomats from violent protesters, anarchists and terrorists while at the same time securing everyone's rights and keeping property intact.
On the waterways, in the air and on land, peacekeeping is a monstrous undertaking for federal, state and local authorities.
"Not just from the security of the event but they have the security in the unique issues in the downtown business district, as well as the rest of the city," said Arnette Heintz, former Secret Service agent. "So, they have three distinct issues that they're going to be addressing during this time period."
The ex-secret service official's firm was hired by Chicago to act as special security advisor.
The U.S. Secret Service is actually in command after the NATO summit was designated a national special security event, which also brings in numerous federal agencies including the FBI.
"You have a bigger mix of potential threats coming together in Chicago to do things and separating those who may want to express their anti-government or their anti-corporate America or anti-whatever it might be. Iin there is somebody who wants to do bad things and looking for those people and preventing them is really the key," said Robert Grant, FBI Chicago.
"Obviously the worst case scenario is a terrorist attack," said Garry McCarthy, Chicago Police superintendent.
Even as thousands of Chicago police officers under Superintendant McCarthy secure city streets and deal with protesters, McCarthy is troubled by the looming possibility of al-Qaeda targeting 60 visiting heads of state and foreign ministers.
"Having been familiar with the biggest one on our soil, I can tell you that it's not something you can train for," said McCarthy. "What you can train for is emergency evacuations, rescue operations and so on."
"This is a target rich environment. Terrorists would like to kill, maim or do anything they possibly could to any and all of these heads of state," said Thomas Mockaitis, DePaul University professor.
But with the layers of heavy security, Mockaitis says the greatest threat is from extremists.
"The planned violence of anarchists who are here to really take advantage of the situation and hide among legitimate protestors," he said.
Thousands of expected protesters who could provide good cover. And if training provided to members of the Occupy movement is any indication, they are preparing for arrests.
During a Grant Park session last fall and similar training last Sunday entitled "How to Disarm a Police Officer," activists were taught how to interact with police on the front line.
"It's not law enforcement. It's war," said Jerry Boyle, National Lawyers Guild. "You can use a show of force, too. You decide when and how you're going to have a confrontation, don't let them decide it for you."
"You plan for it, you prepare for it, you continue to see that your resources are in a place where if something does happen you respond to it to minimize it."
There will be thousands of Chicago police guarding the NATO perimeter, at downtown checkpoints and along Michigan Avenue, with Secret Service agents and National Guard troopers escorting dignitaries from Mag Mile hotels to McCormick Place and federal sharpshooters positioned along transport routes.
