Lingo is an open source software system for automatic indexing of german language documents. The development was determined by the aspects of flexibility, easy configuration, and different applications. The contribution deals with the advantage of a linguistic based automatic indexing system which will improve information retrieval. The available linguistic functionality of lingo is presented and explained via examples. Stemming, recognition and separation of composite words, lexical and algorithmic recognition of phrases and correction of OCR defaults are indicated too. Lingo's open system architecture, possible fields of application, and their boundaries are described.