Law dictionaries are important aids in communicative and cognitive usage situations. By regarding online dictionaries as information tools in a functional theoretical framework, lexicographers have a sound basis for designing online law dictionaries. Dictionaries that provide help to translate from Danish into English should contain data that match the factual and linguistic user competences, user needs and usage situations and should therefore include data about Danish, UK English, US English and international legal terms, their grammatical properties, and their potential for being combined with other words in collocations, phrases and sentences. Data items that deal with these aspects are necessary for Danish users translate subject-specific and register-specific texts into a foreign language. The theoretical aspects discussed and supported by prototypical examples from the planned online dictionaries illustrate the importance of having a sound theoretical basis when making practical information tools. The dictionaries allow users to search the database containing carefully selected lexicographic data depending on what type of help users are looking for, and the search results provide users with different data depending on the usage situation.