If you are a devotee of police uniforms, Istanbul right now is the place to be.
By Jonny Dymond
BBC correspondent in Istanbul
Around the major hotels, littered throughout the centre of the city, on busy road junctions and on the road to and from the airport, the police are everywhere.
Checkpoints are slowing journeys around the city
It is difficult and probably foolish to try to generalise about the mood in a city as large as Istanbul; those with the good fortune to live and work in the part of the city that sits in Asia could go about their business over the next few days, perhaps unaware that there is a summit happening at all.
But across the Bosphorus - shining blue in the hazy summer sunshine - in the middle of the city, it is a very different story.
On the Bosphorus itself, Turkish warships steam up and down, their grey hulls providing a cheerless contrast to the rusty tankers, cruise ships and ferries that normally go up, down and across the water.
Police helicopters - a rarity in Istanbul - swoop over the city; journeys around the centre of town close to the conference centre and the biggest hotels which would normally take five minutes can now take up to an hour.
Concrete blocks, designed to stop suicide bombers crashing explosives-laden vehicles into buildings have appeared as if from nowhere around apparently sensitive sites.
No-one really knows whether this incredibly high-profile operation will work.
It is not just about the dollars and euros that will be spent here by the Nato visitors - it is about affirming Istanbul and Turkey's place in the world
Nerves were set on edge on Thursday when two small bombs went off in Ankara and Istanbul. They were not the kind of attacks that most people were worried about and planning for; and one of them got close to the hotel President Bush will be staying in.
The response of the authorities to the different threats they face has been to "flood the zone" with police and to some degree close it down to all but those lucky or unlucky enough to have Nato accreditation swinging from their necks.
You might expect the residents of the city to be cursing the summit which has already disrupted their lives so much. But there has been little of that kind of attitude.
There are two reasons. First, the people of Turkey are fabulous hosts, generous to a fault and easygoing to the point that you sometimes wonder how anything gets done.
The summit follows a period of things going well for Turkey
Secondly, there is intense pride about the fact that the world is coming to Istanbul. After decades of rather dour semi-isolation, Turkey is on the map.
It is not just about the dollars and euros that will be spent here by the Nato visitors. It is about affirming Istanbul and Turkey's place in the world.
For the past few years now, things have seemed, rather against some people's expectations, to have been going right for Turkey.
The economy is on the mend, the war in Iraq was less painful than many thought it might be, the messages the country is getting from the EU are positive.
And now Nato is coming. No wonder tens of thousands of police officers line the streets keeping watch. This is Istanbul's moment. The authorities will do everything they can to stop anyone spoiling it.