By the year 1555, the catholic kingdom of France affronted the settlement of Churches "being reformed according to the Gospel". Being on conflict with many subjects, Catholic and Reformed nevertheless mutually recognize baptism received in the opposite confession. Focusing on the Western synodal provinces, this thesis explores the reality of mutual recognition and the contribution of baptism to the reformed identity. On the one hand, the study concerns texts (Confession of Faith, Church Order, the Baptism's Form, catechisms, sermons) as well as religious controversy. On the other hand, the study examines baptismal practice bu baptism records, consistoty records and synod proceedings, egodocuments and the royal regulation. Where in the beginning the principal tensions concern catholic baptism ceremonies, later on, they cristallize on catholic doctrine of the absolute necessity of baptism for infants' salvation, revealing in the meantime internal discordance amongst the Reformed. The 'ritual' of baptism, according to texts and observational writings reveals a sobre liturgy. The presentation of infants by godparents is submitted to several rules being surveyed by the consistories, which make it contribute to community cohesion. Baptismal records reveal some typical vocabulary and godparent models ; the supposed preference for Old Testament given names could only partially be confirmed. The King used baptism as an instrument to bring the Reformed back to the Catholic faith, before banning it by the edict of Revocation (1685)