The Orthodox Church is one of the three main Christian groups (the others being Roman Catholic and Protestant). Around 200 million people follow the Orthodox tradition. (...) The nominal head of the Eastern Orthodox Churches is the Patriarch of Constantinople. However, he is only first among equals and has no real authority over Churches other than his own. 
The Eastern Orthodox have no supposedly infallible figure like the Roman Catholic pope; instead, councils of leading churchmen make decisions on matters of faith. The patriarch in Constantinople speaks for the Eastern orthodox worldwide but has nowhere near the authority of the pope in Rome. Orthodox faith tends to be very traditional as well as patriarchal.