Abstract. MiDiLiB is a six year research project on digital music libraries funded by the German Research Foundation (DFG) as a part of the Distributed Processing and Delivery of Digital Documents (V3 D2 ) research initiative. MiDiLiB’s main focus is the development of contentbased retrieval algorithms for both score- and waveform-based music. In this paper we give an overview of our research results, describe several prototypical systems for content-based music retrieval which have been developed during the project, and discuss applications of the presented techniques in the context of today’s and future digital music libraries.