Introduction: We aim to create an in-depth understanding of how pupils in upper secondary school negotiate the credibility and authority of information as part of their practices of learning. Particular focus is on the use of user-created resources, such as "Wikipedia", where authorship is collective and/or hard to determine. Method: An ethnographic study was conducted in an upper secondary school class. Methods included observation, group interviews and information seeking diaries in the form of blogs. Analysis: The empirical material from the class room study was categorised and aggregated into five themes, which emerged as a result of the interplay between the empirical material and a perspective based in socio-cultural theory. Results: The pupils make credibility assessments based on methods developed for traditional media where, for instance, origin and authorship are important. They employ some user-created sources, notably "Wikipedia", because these are easily available, but they are uncertain about when these sources should be considered credible. Conclusions: In an increasingly diverse media world, pupils' credibility assessments need to be informed by a socio-technical understanding of sources which takes both social and material aspects into account. The diversity of resources requires that pupils assess credibility for the particular situation in which they use information.