For Hans Blix, the UN's chief weapons inspector, gaining admission to Iraq may turn out to be the easy bit. Once there, he faces the near-impossible task of ensuring, to everyone's satisfaction - especially that of the Washington hawks - that Iraq no longer has weapons of mass destruction.
Since his appointment more than two years ago, the 74-year-old Swede has had time to pore over documents from previous inspections and plan his strategy.
But Iraq has had almost four years since the last inspectors left to plan its response and, if it has anything to hide, to work out the best means of concealment.
Once inside Iraq, inspectors would visit suspect sites from a list of 700 drawn up on the basis of information inherited from previous inspections or provided by national intelligence agencies and defectors.
Then, within 60 days, they would present the Iraqi government with a plan for continuing their investigation.
Within six months they would be expected to reach preliminary conclusions about whether Iraq is developing weapons of mass destruction.
The previous inspections agency, Unscom, became embroiled in a cat and mouse game with the Iraqi authorities, who tailed the inspectors, tried to work out where they were heading, and sometimes delayed them long enough for sites to be "cleaned".
The new team - the UN monitoring, verification and inspection commission (Unmovic), set up in 1999 - claims the right to inspect anywhere, at any time, without warning. Iraq fears this could lead to unreasonable behaviour and confrontations that would give the US a pretext to launch a military onslaught.
"We certainly feel there is a right to undertake inspections on a Friday, or on a holiday or during the night," Mr Blix told the Guardian newspaper in London earlier this year. "But we do not see any need to undertake any unnecessary provocations." Unlike previous inspectors, who were seconded to the UN by governments, the Unmovic staff are employed directly by the UN - a move intended to address Iraqi complaints that the earlier inspections were used as a cover for spying.
The inspectors consist of two teams, one based in New York and the other in Vienna.
The New York operation, under Mr Blix, is charged with looking for evidence of biological and chemical weapons and long-range missiles. The team in Vienna is part of the International Atomic Energy Agency, now headed by Jacques Baute, and is responsible for hunting any signs of a nuclear weapons programme.
The New York-based team has a workforce of 63 experts from 27 different countries, including 10 women.
If the inspectors uncover anything new, no matter how small, suspicions of major concealment will be aroused and the inspections could become bogged down again.
Mr Blix admits that Iraq hoodwinked him before. He was head of the IAEA in the 1980s when it failed to detect the advanced nuclear weapons programme.
"It's correct to say that the IAEA was fooled by the Iraqis, but the lesson was learned," he told an interviewer. "Not seeing something, not seeing an indication of something, does not lead automatically to the conclusion that there is nothing." - (Guardian)