On May the 1st Pagans celebrate the festival of Beltane. When I was young we simply called it May Day (but that we before Pagans felt comfortable enough to come out of the broom closet!)
May 1st marked the first day of Summer. The new growth of plants and seeds is well under way, so the purpose of the spring festivals has been fulfilled. In summer, therefore, the underlying theme is one of fertility and abundance, with protection for the coming year.
Now it's the fertility bit that causes some modern Pagans a few problems. Personally I think fertility can mean a lot of things - you can have a fertile imagination, for instance. But for some people fertility just means sex. So it's not unknown for Pagans to go along to a Beltane celebration involving people they don't actually know very well, and end up running off into the night screaming when everyone starts taking their clothes off!
You have been warned. 
But actually, there's a lot more to May Day/Beltane than that!
