The EU has no formal connection to any religion. The preamble to the Treaty on European Union mentions the “cultural, religious and humanist inheritance of Europe”. Discussion over the draft texts of the European Constitution and later the Treaty of Lisbon included proposals to mention Christianity or a god, or both, in the preamble of the text, but the idea faced opposition and was dropped.

Christians in the European Union are divided among members of Catholicism (both Roman and Eastern Rite), numerous Protestant denominations (Anglicans, Lutherans, and Reformed forming the bulk of this category), and the Eastern Orthodox Church. In 2009, the EU had an estimated Muslim population of 13 million, and an estimated Jewish population of over a million. The other world religions of Buddhism, Hinduism, and Sikhism are also represented in the EU population.

According to new polls about religiosity in the European Union in 2015 by Eurobarometer, Christianity is the largest religion in the European Union. Catholics are the largest Christian group, accounting for 45.3% of the EU population, while Protestants make up 11.1%, Eastern Orthodox make up 9.6%, and other Christians make up 5.6%.

Affiliation	% of EU population
Christian	71.6
Catholic	45.3
Protestant	11.1
Eastern Orthodox	9.6
Other Christian	5.6
Muslim	1.8
Other faiths	2.6
Irreligious	24
Non-believer/Agnostic	13.6
Atheist	10.4

Eurostat’s Eurobarometer opinion polls showed in 2005 that 52% of EU citizens believed in a god, 27% in “some sort of spirit or life force”, and 18% had no form of belief.

Many countries have experienced falling church attendance and membership in recent years. The countries where the fewest people reported a religious belief were Estonia (16%) and the Czech Republic (19%).The most religious countries were Malta (95%, predominantly Roman Catholic) as well as Cyprus and Romania (both predominantly Orthodox) each with about 90% of citizens professing a belief in their respective god.

Across the EU, belief was higher among women, older people, those with religious upbringing, those who left school at 15 or 16, and those “positioning themselves on the right of the political scale”.

Source: Wikipedia, https://en.wikipedia.org/wiki/European_Union#Religion (10.01.2020)