The Catholic Church on the territory of Moldavia and Bukovina developed throughout the ages on the foundations of early Christian communities in apostolic times. Small Wallachian – Moldavian bishoprics, which were established in various times in history and which now no longer exist, bear testimony to a multi-language and multi-ethnic reality of Moldavia and Bukovina. These church institutions, diverse in the aspect of ethnic genesis, dependant on neighbouring political and church authorities, testify to a universal character of the Catholic Church, which crosses national, ethnic and linguistic boundaries. In the first millenium since the historically proven presence of St. Andrew the Apostle, the church organisation in the Danube provinces developed under the aegis of the Roman bishops. The bishoprics of Cuman (1227-1241), Seret (1371-1434), Baia (1413-1523) and Bacău (1607-1818) are a testimony of common roots of contemporary European culture and constitute a foundation for the19th century church organisation in the Bukovina region under the rule of the Habsburg Monarchy. The article constitutes an attempt at a chronological synthesis of church history in the eastern part of contemporary Romania, embracing six historical periods. Each period is related to institutionally established structures of church organisation on the territory of medieval Moldavia and contemporary Bukovina, organically connected with the Lviv Archdiocese since 1796. Further on, a detailed analysis of social and cultural changes on the backround of historical events shows the invaluable contribution of Polish clergy in introducing a unified church organisation in Moldavia as well as – in later times – in the Bukovina region.