The Web is the largest human information construct in history and it is transforming society (O'Hara and Hall 2008). Understanding what the Web is, engineering its future, and ensuring its social benefit necessitate new interdisciplinary approaches and research methodologies. Web Science (http://webscience.org/webscience.html) is a new interdisciplinary field that studies the Web as both a piece of engineering and infrastructure (micro level) and a phenomenon that impacts society and human activity (macro level). Web Science employs interdisciplinary research approaches (Berners-Lee et al. 2006, Hendler et al. 2008). Due to the size and the dynamicity of the Web, we may consider it as a complex natural phenomenon that deserves to be studied as such, with the help of all classical means used by the natural sciences (observations, experiments, simulations, models, abstractions, generalizations, interpretations, forecasts). At the same time, the Web represents also the first realistic natural laboratory for controlled experiments on human behavior especially when humans (and machines) perform the highest intellectual activities of information processing; studying the ways in which the Web transforms society and human activity thus requires the use of interpretative approaches found in social sciences. Modeling and analysis of theWeb also requires formalisms from computer science, mathematics and statistics.