Music retrieval systems for Western tonal music digital libraries have to consider rhythmic, timbral, melodic and harmonic information. Most existing retrieval systems only take into account melodies. Melody comparison may induce errors since two musical pieces can be very similar whereas their melodies may differ in a significant way. In this paper, we propose to investigate and experiment a retrieval system based on the comparison of chord progressions. The definition of chords may be ambiguous but their properties can be precisely described and represented. We detail the adaptations of alignment algorithms, successfully applied for the estimation of symbolic melodic similarity, for chord progression retrieval. Several experiments, performed on symbolic databases, show that the system described is robust to variations and outperforms a recent chord retrieval system. Categories and Subject Descriptors H.5.5 [Information Systems]: HCI—Sound and Music Computing General Terms Exper...