Forms, guns and questions

Ben Gurion Airport near Tel Aviv has some of the tightest security in the world. Entry forms are stamped on arrival and handed over on departure - although passengers are simply asked to fill in another if the original is lost.

Departing tourists are sometimes outraged at being grilled before their flight, and being asked whom they met in Israel and whether they had any contacts with Arabs. But recently there have been calls for even more precautions.

Foreigners are sometimes searched, but Jews and those with Israeli passports - who made up the majority of passengers from Israel - often go unchallenged.

A spokesman for El Al, Israel's national airline, which has armed marshals on its flights, said it was "investing in new technology to thwart any threat to our passengers".

Visitors to the US, meanwhile, must fill in a form promising they will behave while in the country. All the terrorists who took part in the 11 September attacks will have done so.

The biggest change has been the introduction of the visa waiver programme in 1988, where citizens of "trusted" countries such as Britain enter without a permanent visa if they are staying for three months or less. The waiver is a green form handed out before landing; the bottom third is stapled to the passport. It is removed on departure, usually at the airline check-in desk.

The system is paper-based, so it takes months to find out if a visitor is still in the country.