Résumé : The present study introduces the concept of a mother–infant group therapy that makes use of music, singing, and moving to establish maternal–infant intersubjectivity. It was conducted in a residential mother–baby unit for mothers with postnatal depression and their infants over a 5-week period. Maternal–infant intersubjectivity of four dyads in relation to the group dynamics were microanalyzed for Sessions 1 and 5. We made within-session (i.e., beginning–middle–end) and between-session (Session 1 vs. Session 5) comparisons for the number of intersubjectivity moments (ISMs), total time of intersubjectivity (IST), and the mean duration of ISMs on a dyadic (i.e., own mother/infant involved) and a nondyadic level (i.e., own mother/infant not involved). In addition, three ISM levels (degree of group contribution) were distinguished. The results indicated a significant increase of ISMs/IST from Session 1 to Session 5. Within-session analyses showed that ISMs/IST significantly decreased through Session 1 and remained stable throughout Session 5. Intersubjectivity occurred mainly on ISM Level 1 during Session 1 and on ISM Level 3 during Session 5, suggesting increased dyadic autonomy and self-efficacy. The results are discussed in relation to the musical characteristics of mother–infant dyads, music improvisation techniques, group processes, and intersubjective development.