Based on the numbers of adherents, the Eastern Orthodox Church (also known as Eastern Orthodoxy) is the second largest Christian communion in the world after the Roman Catholic Church. The most common estimates of the number of Eastern Orthodox Christians worldwide is approximately 220 million baptised members,[1][2][3] The numerous Protestant groups in the world, if taken all together, substantially outnumber the Eastern Orthodox,[4] but they differ theologically and do not form a single communion.[5]