While officials say there are no specific, credible terror threats, security will be far more intense in New York than it was at the Democratic Convention in Boston.
"New York City is being well protected, on land, at sea, and in the air," says Mayor Michael Bloomberg.
Protecting an incumbent president, officials say, is a more complicated mission. And this convention comes closer to the election, which intelligence analysts say al-Qaida seems determined to disrupt.
Nearly 15,000 police and federal agents will be on duty -- intensively patrolling what they call "the frozen zone" around Madison Square Garden and keeping close guard on the two dozen delegate hotels.
Snipers will watch from rooftops, aided by helicopters, while harbor patrols guard bridges and landmarks and Air Force jets circle overhead the entire week.
And the Secret Service is sealing off access to the water from an adjacent building that helps chill the convention hall's air supply.
With fears high of a Madrid-style attack, rail service is getting especially close attention. This will be the largest mission for bomb-sniffing dogs in New York history, checking every train that comes into Penn Station.
The station itself, beneath the convention site, will remain mostly open, because it's the equivalent of five stories underground.
With nearly a quarter-million protestors expected, police have been trained to arrest crowds that become violent. Some officers will even be equipped with TV cameras in their riot helmets, part of the stream of nearly 400 video sources feeding into the main command center, staffed by 116 people from 66 separate agencies.
"It's a very complicated scenario to protect. But they've been working on it for about 18 months, and I'm pretty confident they've done everything they need to do provide a safe and secure convention," says Homeland Security Secretary Tom Ridge.
With so much to watch and worry about, the Secret Service says this will be the biggest public security mission ever, and the toughest.