For this study, we will present the most important ecumenical activities of Patriarch Justinian Marina. He was the third Patriarch of the Romanian Orthodox Church between 1948 and 1977. During this period, he was very concerned to establish a relationship with the main ecumenical institutions. We will speak about his dialogue with one of the most important ecumenical group, namely the World Council of Churches, founded in 1948 in Geneva, Switzerland. Of course, the dialogue with the Church of England must (...) to be mentioned. His ecumenical activity was very important for the Orthodox Church, Patriarch Justinian being one of the most important Church leaders who tried and succeeded to be in contact with different religious leaders from Romania and abroad. We do not have to forget that during his time the communist regime ruled our country. In the first part, we will give different historical information about his ecumenical activity and in the second part we will explore his theological thinking about the ecumenical dialogue and movement. (shrink)