The decline of Christianity is an ongoing trend in Europe. Developed countries with good educational facilities in the post-World War II era have shifted towards post-Christian, secular, globalized, multicultural and multifaith societies. Infant baptism has declined in many nations, with thousands of churches closing or merging due to lack of attendees. There is also evidence of decline in North America. Despite the decline, Christianity remains the dominant religion in the Western world, where 70% of the population is nominally Christian.
Scholars have proposed that Church institutions decline in power and prominence in most industrialized societies, except in cases in which religion serves some function in society beyond merely regulating the relationship between individuals and God.
Reports are mixed on the extent and rate of the decline of Christianity. A 2015 analysis of the European Values Study in the Handbook of Children and Youth Studies identified a "dramatic decline" in religious affiliation across Europe from 1981 to 2008. However, Christianity is still the largest religion in Western Europe, according to a 2018 study by the Pew Research Center, where 71% of Western Europeans identified themselves as Christian. According to the same study, 83% of those who were raised as Christians still identify as such. The European Values Study found that in most European countries in 2008, the majority of young respondents identified themselves as Christians. Unlike Western Europe, in Central and Eastern European countries the proportion of Christians has been stable or even increased in the post-communist era.
In 2017, a report released by St. Mary's University, London concluded that Christianity "as a norm" was gone for at least the foreseeable future. According to the report, 91% of people in the Czech Republic between the ages of 16 to 29 have not declared a religious affiliation, and in the United Kingdom , only 7% identify as Anglican (compared to 6% who identify as Muslim). In at least 12 out of the 29 European countries surveyed by the researchers, the majority of young adults reported that they were not religious.
In Quebec, since the Quiet Revolution, over 500 churches (20% of the total) have been closed or converted for non-worship based uses. In the 1950s, 95% of Quebec's population went to mass; in the present day, that number is closer to 5%. Despite the decline in church attendance, Christianity remains the dominant religion in Quebec, where 82.2% of people are Christians.
Christianity, specifically Catholicism, remains the dominant religion in the Republic of Ireland. In the 2016 census, 85.1% of the population identified as Christian. However recent social changes, including the lifting of a ban on abortion and the legalising same sex marriage, have solidified the growth of liberal thinking in Ireland, particularly within the younger community. An Irish priest, Fr. Kevin Hegarty, asserted in 2018 that the church's authority was undermined by the papal encyclical, called Humanae Vitae, that established the Church's opposition to contraception. He reported that there is only one priest under the age of 40 in the entire diocese of Killala; only two priests have been ordained over the last 17 years, and there have been no candidates for the priesthood since 2013. Hegarty blames this decline on the Church's positions on female ordination, contraception and sexuality. A continued requirement for children entering Irish Catholic owned schools to be baptized keeps the overall level of baptisms high, though the number of individuals practicing a faith or attending church is at an all time low and rapidly decreasing.
Starting in 1880 and accelerating after the Second World War, the major religions began to decline among the Dutch, while Islam began to increase. During the 1960s and 1970s, pillarization began to weaken and the population became less religious. In 1971, 39% of the Dutch population were members of the Roman Catholic Church; by 2014, their share of the population had dropped to 23.3% (church-reported KASKI data), or to 23.7% (large sample survey by Statistics Netherlands in 2015). The proportion of adherents of Protestantism declined in the same period from 31% to 15.5%. With only 49.9% of the Dutch currently (2015) adhering to a religion, the Netherlands is one of the least religious countries of the European Union, after the Czech Republic and Estonia. By the 1980s, religion had largely lost its influence on Dutch politics and as a result Dutch policy on women's rights, abortion, euthanasia, homosexuality and prostitution became very liberal in the 1980s and 1990s. As a result of the decline, the two major strands of Calvinism, the Dutch Reformed Church and the Reformed Churches in the Netherlands, together with a small Lutheran group, began to cooperate as the Samen op weg Kerken ("Together on the road churches"). In 2004 these groups merged to form the Protestant Church in the Netherlands.
In 2015, Statistics Netherlands found that 50.1% of the adult population declared themselves non-religious. Christians comprised 43.8% of the total population, of whom 23.7% were Catholics; 15.5% Protestants; and 4.6% members of other Christian denominations. Followers of Islam comprised 4.9% of the total population, Hinduism 0.6%, Buddhism 0.4% and Judaism 0.1%.
The proportion of the population following Islam has increased, primarily via immigration. In the early 21st century, religious tensions between native Dutch people and migrant Muslims was increasing. After the rise of politician Pim Fortuyn, who sought to defend the Dutch liberal culture against what he saw as a "backwards religion", stricter immigration laws were enacted. Religious tensions increased after the murder of Pim Fortuyn in 2002, as well as the 2004 assassination of Theo van Gogh by Mohammed Bouyeri, a conservative Muslim.
In December 2014, for the first time, there are more atheists (25%) than theists (17%) in the Netherlands. Currently the majority of the Dutch population is agnostic (31%) or spiritual but not religious (27%).
In 2015, 63% of Dutch people think that religion does more harm than good. A quarter of the population thinks that morality is threatened if no one believes in God, down from 40% in 2006. The number of people reporting that they never pray rose from 36% in 2006 to 53% in 2016.
Adherence to established forms of church-related worship is in rapid decline in Spain and Italy, and Church authority on social, moral and ethical issues has been reduced. In 2017, the PBS News Hour reported that Seville's historic cloistered convents were suffering from Christianity's decline in Spain .
Despite the decline of daily attendance and the church's authority, Catholicism remains the dominant religion in Spain and Italy. According to the Spanish Center for Sociological Research, 68% of Spaniards self-identify as Catholic in 2019, and according to Pew Research Center, 83.3% of Italy's residents are Christians.
Attendance at Anglican churches had started to decline in the UK by the Edwardian era, with both membership in mainstream churches and attendance at Sunday schools declining. The UK experienced a further decline in infant baptisms after World War II. In 2014, Archbishop of Canterbury Rowan Williams stated that the UK had become a "post-Christian country." That same year, only 4.3% of the population participated in a Church of England Christmas service. Despite the decline, according to the 2011 Census, Christianity is the majority religion, and around 60% of all respondents identified as Christians.
Christianity is the largest religion in the United States . In 2016, Christians represented 73.7% of the total population. In 2019, Christians represented 65% of the total population.  Nationwide Catholic membership increased between 2000 and 2017, but the number of churches declined by nearly 11%. The Evangelical Lutheran Church in America (ELCA) lost about 30% of its congregation and closed 12.5% of its churches: the United Methodist church lost 16.7% of its congregation and 10.2% of its churches. The Presbyterian Church has had the sharpest decline in church membership: between 2000 and 2015 they lost over 40% of their congregation and 15.4% of their churches. Infant baptism has also decreased; nationwide, Catholic baptisms are down by nearly 34%, and ELCA baptisms by over 40%.
In 2018, the Minneapolis Star Tribune reported that churches in Minnesota were being closed due to dwindling attendance. Mainline protestant churches in Minnesota have seen the sharpest declines in their congregations. The Catholic Church has closed 81 churches between 2000 and 2017; the Archdiocese of Minneapolis closed 21 churches in 2010 and has had to merge dozens more. In roughly the same time frame, the Evangelical Lutheran Church in America in Minnesota has lost 200,000 members and closed 150 churches. The United Methodist Church, which is Minnesota's second-largest Protestant denomination, has closed 65 of its churches. In the early 1990's, the Archdiocese of Chicago closed almost 40 Catholic churches and schools.  In 2016, increasing costs and priest shortages fueled plans to close or consolidate up to 100 Chicago Catholic churches and schools in the next 15 years. 
Moderate and liberal denominations in the United States have been closing down churches at a rate three or four times greater than the number of new churches being consecrated. However according to The Christian Century, the rate of annual closures is approximately 1% and quite low relative to other types of institutions. It has been asserted that of the approximately 3,700 churches that close each year, up to half are unsuccessful new churches.
Denominations like Jehovah's Witnesses, The Church of Jesus Christ of Latter Day Saints, and Eastern Orthodox have had slight increases in membership between 2003 and 2018. Nevertheless the number of adults in the United States who do not report any religious affiliation nearly doubled over that period. In 2017, Schnabel and Bock argued that while "moderate religion" has declined in the United States since the late 1980s, "intense religion" including evangelicalism has persisted.