Enterprise 2.0 can be defined in an admittedly cryptic way by saying it is the use within the corporation of a set of participative technologies known under the buzzword Web 2.0. What I want to do in this article is to proceed in the way of peeling an onion, starting with the external effects of Web 2.0 on society and business, then moving toward the interface of communities and corporations, and lastly to discussing some internal effects of Enterprise 2.0 on the corporation.