In order to navigate huge document collections efficiently, tagged hierarchical structures can be used. For users, it is important to correctly interpret tag combinations. In this paper, we propose the usage of tag groups for addressing this issue and an algorithm that is able to extract these automatically for text documents. The approach is based on the diversity of content in a document collection. For evaluation, we use methods from ontology evaluation and showed the validity of our approach on a benchmark dataset. 1 How to tag When searching for information, structured access to data, e.g., as given by web directories or social tagging systems like del.icio.us can be very helpful. The goal of our work is to automatically provide such structure for unstructured collections. For this, we automatically tag text documents based on their content. We do not tag resources individually, but compute the tags collection based. By this, we can directly aim at supporting efficient browsing by...