Dictionaries contain a wealth of linguistic data which, given the customary alphabetical arrangement encountered in most cases, are neither readily accessible to the user nor susceptible to control by the lexicographer. The present volume sets out the most important types of covert lexicographic data, dicusses ways of improving access to them by means of philologically organised indexing systems, illustrates these possibilities with the help of copious examples and thus provides a key for the exploitation of covert lexicographic information both for language-historical research purposes and for the improvement of lexicographic practice.