Atheists have traditionally been seen as rather joyless. Perhaps it's because their defining characteristic is being against something, which does give you the sense of being rather negative. "What do we want?" is a rallying call, "What don't we want?" just sounds a bit grumpy, and not entirely grammatical.

And as the rationalist movement gains ground, accusations of bullying and sour-faces abound: Richard Dawkins picks on fundamentalist idiots, not high-end theologians, Martin Rowson draws spiteful cartoons about Muslims and Christians and it isn't fair.

Now the atheists have begun to hit back: they want to be seen as positive. And why not? They haven't nailed many people to crosses, or stoned many women to death for the crime of having been raped. In recent years, to my knowledge, they've watched box sets of The Wire, made gingerbread and gone to the pictures. They've pointed out, as politely as they can, that not believing in God isn't the same as not practising many virtues that plenty of religious people hold dear. Plenty of atheists have been kind, generous and patient, and not in the hope of reward in the afterlife, but just because they've noticed that being decent is pleasurable and easy.

The atheist banner has become an alluring one for plenty of people who don't normally do groups, mainly thanks to the efforts of a few flag-wavers: Caspar Melville, at The New Humanist Ariane Sherine (who orchestrated the Atheist Bus Campaign, in response to aggressive Christian adverts) and Robin Ince, who organised the Nine Lessons and Carols for Godless People shows in London last year.

And now we have The Atheist's Guide to Christmas, edited by Sherine and likely to create as much of a buzz as her bus adverts. The book's contributors include Derren Brown, Charlie Brooker, Simon Singh, A. C. Grayling and even Simon Le Bon, whom I last saw being waterboarded in the Wild Boys video.

There are some God-baiting essays in it, including a Wodehouse pastiche from Professor Dawkins. But most atheists don't give much thought to religion at all. We occasionally get riled at religious schools teaching creationism, or religious spokesmen in telling us that, because they believe life is sacred, we have to die in agony. But we don't sit cackling in our cellars, wondering where to get a goat to sacrifice, and we don't believe in Black Magic, unless it's chocolate.

Most of the book simply reveals that many people who don't do God love to do Christmas. Claire Rayner writes extensively on the many pagan traditions wrapped up in a modern Christmas. Josie Long offers an array of games and crafts to would keep the most petulant Scrooge entertained.

But above all, Atheist's Guide shows a new side to the rationalist movement. For a start, it gives room even to those who are technically agnostic, like me. I long for an agnostic bus campaign, pondering the unknowability of buses, before deciding that the 38 might get us home whether it exists or not. Second, it shows that atheists are actually for something - fun, kindness, pleasure, charity and scientific wonder. The late Douglas Adams summarised the position perfectly when he asked: "Isn't it enough to see that a garden is beautiful without having to believe there are fairies at the bottom of it too?" This is our gardening manual.

The Atheist's Guide to Christmas is published by The Friday Project (£12.99). Proceeds will go to the Terrence Higgins Trust.