The interpersonal world assumes a rapid, dynamic, reciprocal, body-present exchange with whom we interact. Adults are often responsive to infant behavior from the first months of life and thus scaffold their learning of interpersonal reciprocity. Certain adult responses involve some kind of matching of the behavior of the infant. Maternal imitation and affect attunement are two recognized matching activities that set a special degree of intersubjectivity and mutuality. In this chapter we present a single case study of a mother-baby dyad where we analyze both matching activities between the 2nd and 10th month of the life of the infant. Maternal imitation is a phenomenon widely studied in cognitive developmental psychology; affect attunement, on the other hand, despite being a recognized phenomenon, has been scarcely researched empirically. Our research offers novel empirical data on affect attunement, and findings on imitation in dialogue with previous studies. We focus on the development of maternal imitation and affect attunement frequencies; on the temporal coordination between infant behavior and adult response, and the pairing between the behavioral modalities of the baby and the mother (vocalization, facial expression, movement).