Tvärslå is a dynamically expandable multilingual on-line dictionary, composed of all dictionaries used and developed in the Nordisk netordbog (Nordic Web Dictionary) project. Currently the languages included are Swedish, Danish, Norwegian, Icelandic, Finnish and English. Tvärslå can be used both interactively and called by the Tvärsök system [1]. This article describes the functionality of Tvärslå and how the system was constructed, beginning in choosing an XML format suitable for exchanging dictionaries within the project.