This article wants first of all to describe, which historical-theological factors contributed to an important shift of meaning of the concept of conversion from the 18th and 19th century onwards. A more communal and covenantal, theocentric and ecclesial understanding of religious belonging has gradually shifted towards an individual personal, experiential, anthropocentric and charismatic interpretation. Evangelicals and Pentecostals share the idea of 'heartfelt religion', interpreting conversion as a sudden and momentous event, usually after a personal crisis. The historical churches rather stress the lifelong challenge of conversion, related to participation in church life, the liturgy and the sacraments.The second part deals with a series of Roman Catholic-Pentecostal ecumenical dialogues about the problems arising between these rather opposite ideas of Christian conversion. Different ecclesiological and pneumatological points of view are at stake here. Major problems arise when people from the older churches are invited to change their affiliation and want to renew their baptismal votes with the 'baptism in the Holy Spirit'. Dialogue partners tend to avoid all forms of proselytism, but common evangelisation and common witness, let alone ecumenical cooperation toward church unity or ecclesial communion still seem to be a bridge too far.