While the primary INEX test collection is based on a single DTD, it is realistic to assume that most XML collections consist of documents from different sources. This leads to a heterogeneity of syntax, semantics and document genre. In order to cope with the challenges posed by such a diverse environment, the heterogeneous track was offered at INEX 2006. Within this track, we set up a collection consisting of several different and diverse collections. We defined retrieval tasks and identified a set of topics. These are the foundations for future run submissions, relevance assessments and proper evaluation of the proposed methods dealing with a heterogeneous collection.