The three main branches of Christianity in the modern world are the Eastern Orthodox Church, the Catholic Church, and Protestantism. Of these three, the Catholic Church is the most monolithic and hierarchical. The Eastern Orthodox Church split with the Catholic Church in 1054, in what is known as the "Great Schism." Protestantism emerged out of Christianity as a result of the teachings of Martin Luther and the Reformation in the sixteenth century.
The Eastern Orthodox Church considers Jesus Christ to be its leader. Beneath Him are bishops, each of whom is the leader of a geographic area. Eastern Orthodox bishops are organized into groups called synods. Each synod is self-regulating and autonomous. While the Pope in Rome was part of this group prior to 1054, since the "Great Schism", Eastern Orthodoxy no longer recognizes the Pope.
The Pope is the leader of Catholicism. The Catholic Church reckons Jesus Christ's disciple Peter to be the first Pope, since Christ conferred authority on him to continue the church after His death. The current Pope is believed by Catholics to be the last in an unbroken line of Popes that began with Peter. Beneath the Pope are cardinals, and beneath them are nearly 3,000 bishops, each of whom oversees a diocese. Beneath the bishops are priests, each of whom is responsible for a parish. Priests are sometimes assisted by deacons.
Following the Reformation, Protestantism did not assume the same monolithic form as Catholicism. Protestantism consists of a large number of sects, including Baptists, Methodists, Presbyterians, Congregationalists, Lutherans and Episcopalians. The Anglican Church is also a Protestant church, but is much more closely associated with Catholicism than other forms of Protestantism. These groups represent a wide variety of interpretations of Christian doctrine, their differences often being the catalysts that split them into different organizations at some point in the past. In general, Protestant churches are distinguished from Catholicism by their belief that Communion is symbolic and doesn't involve true transsubstantiation (the transformation of Communion wafers and wine into the body and blood of Christ), and by de-emphasizing the Virgin Mary in Christian worship.
Mormons, Anabaptists, Seventh Day Adventists, Quakers, Mennonites, Doukhobors and many smaller and lesser known sects are associated with Christianity to greater or lesser degrees. In addition, the lessening of the church's social influence throughout the twentieth century has resulted in a growing number of people who identify themselves as Christians, but aren't members of any church. These people represent the decline of "sacerdotalism," the belief that priests and other authority figures are necessary intermediaries between God and laypeople.