From their website:
On the 17th of September, we want to see 20,000 people to flood into lower Manhattan, set up tents, kitchens, peaceful barricades and occupy Wall Street for a few months. Once there, we shall incessantly repeat one simple demand in a plurality of voices and we will not leave until that demand has been met. Like our brothers and sisters in Egypt, Greece, Spain, and Iceland, we plan to use the revolutionary Arab Spring tactic of mass occupation to restore democracy in America. We also encourage the use of nonviolence to achieve our ends and maximize the safety of all participants.