All this week, I’ll be posting items on Orthodox Christianity, an important but understudied (at least in America) Christian communion. To start, here’s a new report from the Pew Research Center on Religion and Public Life, “Orthodox Christianity in the 21st Century,” released this month. Orthodox Christianity has relatively few communicants in the United States, mostly immigrants from Orthodox countries and their descendants, as well as a small number of converts, especially from Evangelical denominations. But, globally, Orthodoxy is the third largest Christian communion, after Catholics and Protestants, with a combined number in the hundreds of millions.

Orthodox leaders are becoming increasingly visible in global affairs. For example, the Ecumenical Patriarch has been active on environmental questions. Thanks to an increasingly assertive Russian Church, Orthodoxy is beginning to have an impact in human rights fora like the UN Commission. In fact, even in the US, Orthodox Christians may have had an impact on the last presidential election. At a panel at Fordham University earlier this month, scholar Nicholas Gvosdev pointed out that Donald Trump appealed to Orthodox Christians in places like Michigan–which Trump won with a narrow margin.

The Pew report reveals that although their numbers across the globe are growing in absolute terms, the number of Orthodox Christians has declined relative to Catholics and Protestants. In the Middle East, at least, that decline is explained in part by persecution against Orthodox (and other) Christians in the twentieth century, which continues today. Seventy years of Communist repression in the former Soviet Union and Eastern bloc also didn’t help. But the report reveals a hopeful resurgence of Orthodox Christianity in former Communist countries.

The report pays a lot of attention to the largest Orthodox Church outside Europe, the Ethiopian Orthodox Church (36 million members), one of the five so-called Oriental Orthodox Churches. This is commendable, as people often assume that Orthodoxy is an entirely European phenomenon. Although declining in its historic European home, Christianity is soaring in the global south, including in Africa. In fact, the Ethiopian Church, an ancient Christian body without any colonial associations, may be well positioned to do missionary work across the continent in the coming century.

The report details many interesting facts about Orthodox practice and belief — compared to Catholics and mainline Protestants, for example, the Orthodox are deeply conservative on social issues like gender and marriage — as well as prospects for ecumenism. It will be very valuable for anyone interested in the sociology of Christianity today. (H/T: George Demacopoulos at Fordham’s Orthodox Christian Studies Center, who served as a scholarly adviser on the report).