Twenty-five years ago it began in a single tent in Charlotte Square. The very first Edinburgh Book Festival, under its young director, Jenny Brown, was a modest enough affair, which no one thought could be repeated annually, but probably every two years.

Even then, though, it had aspirations. There were 84 authors, and 120 events, including Alasdair Gary, Allan Sillitoe, Emma Tennant, Michael Rosen, Joan Lingard, and a brash young thriller writer called Jeffrey Archer.

Everyone had to pay an entrance fee of a pound, and there were some events that struggled to find an audience. But there was, among those lucky enough to be there, a sense that this was an idea whose time had come.

Fast forward to 2008, and Charlotte Square, this summer will look more like the English encampment on the eve of Agincourt - a sea of canvas and more solid structures, with the addition of offices, cafés, show-rooms, yurts and spiegel tents. There will be 800 authors attending, and 750 events. And yes, it's annual - who can imagine it being otherwise? - and yes, all the aforesaid authors will be back again, and no, they will not include Jeffrey Archer.

For The Times and The Sunday Times to be sponsors of the festival is a great privilege. It puts us at the heart of what is not only a world event, but surely one of the most enjoyable world events to be found anywhere.

Everyone who attends speaks of the inimitable atmosphere created in that square, the pleasure to be had from listening to a favourite writer, watching a keenly-argued debate, or simply drifting in to hear someone whose name you have never heard before but who might, just possibly, become your bedside reading for years to come.

Of course Edinburgh now has its competitors, all across Britain, from Hay-on-Wye to Cheltenham, not excluding Wigtown, and across the world, from Sidney to Las Vegas, from the Zimbabwe International Book Fair to the Smoky Mountain Storytelling Festival.

But, as its current director Catherine Lockerbie, said yesterday, Edinburgh has thrived on the challenge, simply expanding quietly or indeed quite noisily, every year. Quite how it does so without breaking the bounds of Cahrlotte Square, and without losing that sense of intimacy is just one of the tricks that it manages to pull without appearing to try too hard.

We await, once again, the miracle to be achieved this August.

And for readers of The Times, the best place to start preparing for it is right here.

Times Recommends

• Charles blazes trail as sun king
• Thalidomiders win payout 50 years on
• Libel gag on talk of 'medical hurricane'