BBC News Online
It is a mammoth task, by any stretch of the imagination.
GCHQ's new premises cost £370m
Move 4,500 staff, their files, phones, fixtures and fittings - not to mention computers worth millions of pounds - into a new home with as little disruption as possible.
Do all this without switching off any of the hi-tech gizmos and computers that keep the whole place ticking over.
And without taking your eyes and ears off the secret goings-on around the world which it is your job to monitor.
No wonder, then, that GCHQ's move from its current antiquated home in more than 50 small buildings across Cheltenham to a shiny new £337m all-in-one location in the town is set to take about a year.
Three years in the building - and almost a decade in the planning - the Government Communications Headquarters' new home is just about finished.
Spies and boffins will begin transferring to their new offices - nicknamed The Doughnut - in September.
The powers-that-be hope the new building will foster a friendlier, more open working atmosphere in the notoriously secretive government department.
"It will be much easier to communicate effectively and efficiently, and will promote better feedback across a range of issues," explains a spokesman.
The move also marks a huge update of GCHQ's image.
Gone are the dozens of dark Bletchley Park-style sheds populated by shy loners puzzling over mysterious ciphers.
In their place comes a light and airy 21st Century palace of glass, concrete and steel the size of Wembley Stadium, complete with car and cycle parking in concentric rings around the circular building.
Inside, workers at the all-new GCHQ will plug in their laptops in open plan offices and take part in team-building exercises in "break-out areas".
When they have had enough of chasing hackers, dealers and spies, they can enjoy lunch in the four-storey-high glass atrium, or in a landscaped courtyard big enough to hold the Albert Hall.
"The open plan nature of the work areas ensures flexibility to deal with the challenges thrown up by fast-moving and unpredictable threats posed by terrorism, organised crime and other nasties, and the ever-growing sophistication and speed of global communications," says the spokesman.
The Doughnut: facts and figures
Size: 70 feet tall and 600 feet in diameter, on a 176-acre site
Materials: Steel, concrete, glass and Cotswold stone
Special features: An underground road for delivering sensitive post and documents; a courtyard garden big enough to hold the Albert Hall
Architect: Chris Johnson for Gensler
Security is still paramount, of course - members of the public will not be able to wander in off the street.
But the new GCHQ wants at least to be seen to be open - hence job adverts in newspapers, and a website boasting interviews with members of the team.
And this is another of the Doughnut's aims - to encourage today's graduates and jobseekers to choose Cheltenham over London.
"We believe the new site will help us to achieve improved capability and productivity well into the 21st Century," says Dr John Bosnell, GCHQ's programme director.
"The improved working environment will enable us to facilitate modern working practices and will be a long-term aid to motivating, recruiting and retaining staff."
But Dr Bosnell says that although the new HQ will be much more environmentally-friendly than the old multi-site one, there are limits.
"The building will enable us to manage energy more effectively and tale a 'greener' approach, but we do not have plans for an organic garden in the courtyard."