When I am asked by people what is the difference between Orthodoxy and Catholicism, I will either answer “very little” or “a whole lot”, depending on who is the asking and the context of the question.
If the questioner is a Protestant, I will most likely answer the former: very little is different, as least in comparison with the differences between Protestantism and the apostolic Churches. We both have sacraments, authoritative bishops, reverence for Mary, prayers for the dead – and the list could go on quite some time.
If the questioner is a Catholic and knowledgeable about the Faith, I will more likely answer that a “whole lot” is different. The filioque, authority of the pope, purgatory, the Immaculate Conception of Mary – and the list could go on quite some time.
When a Western Christian first explores the East, he cannot get over how alike it is to Catholicism. It seems to be simply a different view of the same beliefs. However, the more one explores the East, the more one realizes that in many ways, the East is not even using the same playbook as the West, and this leads to subtle, yet very important, differences in our views of God and His plan of salvation. Whereas I truly believe that most of these differences are reconcilable, I do accept that they really are differences – Orthodoxy is not simply Catholicism without the pope.
The blog Vivificat!, run by a Roman Catholic who was at one time Eastern Orthodox, has a very nice post which lists 12 beliefs of the Orthodox which are fundamental to their identity but are not consistent with Catholic belief (at least not consistent based on our current understanding of doctrine). Read it here: