The article describes Web 2.0 as a revolutionary technology for actual learning. Using the example of the Wikipedia article about Fukushima, it discusses emergent processes of knowledge building and explains how they can be used for learning purposes. The examples make it obvious that it is the social system that makes groups work so effectively. This system is established through an artifact-centered collaboration, based on specific and self-given rules of knowledge building. This example of cooperation in Wikipedia can serve as a model also for formal education. (Contains 2 figures and 1 footnote.)