WikiQA is a German open domain question answering system that uses the Wikipedia as a knowledge base to answer natural language questions. It has been developed by the KnowCIT project (Artificial Intelligence Group) within the CITEC at Bielefeld University. Using open domain encyclopedic information as a knowledge base, such as provided by the Wikipedia project, has captured the attention of QA researchers lately. However, most of the proposed Wikipedia-based QA systems focus primarily on the document collection of Wikipedia for answer retrieval, and thus disregard the complex hierarchical representation of knowledge by means of its category taxonomy, which can also be valuable in the context of QA systems. The WikiQA system approaches the Wikipedia collection from a different point of view. It exploits the use of the Wikipedia category taxonomy as a reference point for identifying the broader topic of a user’s question, in order to deduce from the topic a set of expected answer candidates. More precisely, it accesses and activates only those areas of our knowledge base which are primarily topically relevant to the questions subject.