For more than one millennium, the East and the West church have been in a state of official schism. The schism of 1054 divided Christians on Catholics, and Orthodox Christians.
In recent decades, leaders of both the Catholic and the Orthodox church have made closer ties a priority, there are still some issues that remain a problem. One of the biggest problems is the authority of the pope.
The Catholic Church defines Papal Primacy, which means that the Bishop of Rome has immediate and direct jurisdiction over the whole Church. On the other hand, the Orthodox Church has a conciliar model of the Church. They believe in unity, and not in centralized authority. The Orthodox Church does not recognize the authority of the Bishop of Rome over all Christians.
This lecture by Fr. Josiah Trenham, details some of the differences between the two churches, and how Orthodox Christians think of the Catholics.
Fr. Josiah Trenham is a Senior Pastor of Saint Andrew Orthodox Church in Riverside, CA.