This paper presents FOLKER, an annotation tool developed for the efficient transcription of natural, multi-party interaction in a conversation analysis framework. FOLKER is being developed at the Institute for German Language in and for the FOLK project, whose aim is the construction of a large corpus of spoken present-day German, to be used for research and teaching purposes. FOLKER builds on the experience gained with multi-purpose annotation tools like ELAN and EXMARaLDA, but attempts to improve transcription efficiency by restricting and optimizing both data model and tool functionality to a single, well-defined purpose. This paper starts with a description of the GAT transcription conventions and the data model underlying the tool. It then gives an overview of the tool functionality and compares this functionality to that of other widely used tools.