It is inevitably partial and generally based on claims by the denominations themselves. The numbers should therefore be considered approximate and the article an ongoing work-in-progress. With about 2.42 billion adherents all over the world, Christianity is the largest religious group in the world.
The list includes the Catholic Church including the Eastern Catholic Churches; all the Eastern Orthodox and Oriental Orthodox churches with some recognition and their offshoots; Protestant denominations with at least 0.2 million members; the provinces of the Anglican Communion with at least 0.2 million members; all the other Christian branches with distinct theologies, such as Restorationist and Nontrinitarianian denominations; the independent Catholic denominations; and the Church of the East.
Protestantism is the second largest major group of Christians after the Catholic Church by number of followers. Estimates vary considerably, from 400 million up to more than a billion. One of the reasons is the lack of a common agreement among scholars about which denominations constitute Protestantism. For instance, most of the sources but not all of them include Anglicanism as part of Protestantism (see below). Moreover, Protestant denominations do not form a single communion, comparable to those of the Catholic Church and Eastern Orthodoxy. Nevertheless, 900 million is the most accepted figure among various authors and scholars, and thus is used in this article. Note that 900 million figure also includes Anglicanism, as well as Anabaptists, Baptists and multiple other groups which have in their scope some denominations that might disavow a common "Protestant" designation, and would rather prefer to be called, simply, "Christian".