The premise of NaNoWriMo is simple: write 50,000 words in the month of November, beginning at the stroke of midnight on the 1st of November and ending at midnight on the 30th. What can you write? Well, the options are as open as your imagination - chick-lit, sci fi, murder mystery, young adult — even erotic fiction is well catered for!
There's no impediment even if you're not too interested in fiction: you can always join the NaNo Rebels and write anything you desire, from biography to self-help, memoirs to poetry.
Even starting without a plot is no impediment to brave and intrepid participants. The battle cry "no plot? no problem!" can occasionally be heard ringing out, which by a not-very-amazing-at-all coincidence is also the name of the self-help book written by NaNoWriMo's founder, Chris Baty.
The basic premise of the event is to encourage you to lower your horizons and start your novel with the theory that quantity, rather than quality, is the most important part. You can polish your novel into gleaming publishability later, but it's all useless if you haven't got a novel to begin with!
So every year, tens of thousands of participants around the world fling themselves with great gusto into the challenge, and every year a vast proportion of that figure cross the finish line with their 50,000 (or more!) words, exhausted, relieved and thrilled.
If you want to find out more, head over to the NaNoWriMo website and browse the site, find forums for your preferred genre and location and take a peek at the FAQs, and above all don't be afraid to sign up and join in!
They say everyone has a book in them (hopefully, for continued participation in NaNo, at least one), so come and explore yours.