Madrid, Spain - Even countries like Ireland and Italy, which have been staunchly Catholic for centuries, have seen sharp drops in the number of Catholics attending church.
The Roman Catholic Church's reputation has been badly hit by a string of paedophile priest scandals, as well as decades of creeping secularisation, in which the Vatican has dismayed many Catholics with its conservative views on issues such as women priests, gay marriage, artificial contraception and abortion.
In Spain, Jose Luis Rodriguez Zapatero, the prime minister, has clashed with the Church over abortion and changed the law to make it easier for women seeking to terminate unwanted pregnancies.
Around 80 per cent of Spaniards identify themselves as Catholics but two-thirds seldom or never attend church.
Less than 50 per cent of Irish go to Mass at least once a week, compared with 85 per cent two decades ago, with many Catholics left shocked and angry over the decades-long cover-up of sexually abusive priests.
In Italy, where more than 95 per cent of people describe themselves as Catholic, church attendance has fallen to less than 30 per cent.
Catholic churches and chapels in France are also increasingly empty and cathedrals are visited more by tourists than by the faithful.
Catholicism is also in decline in the United States, where 400,000 people left the Church in 2008 alone.
Even in Latin America, the Church has been hit by sex scandals in countries such as Brazil and Mexico.
The picture is much brighter in Africa and Asia, where Catholicism is on the rise. The number of Catholics in Africa tripled between 1980 and 2010, from 55 million to 150 million.
In Asia, church membership increased by 80 per cent in the same period. African and Asian countries now supply priests to Europe, in a reversal of centuries of missionary activity.
Benedict XVI has said that confronting the decline of Catholicism in Europe is one of the biggest priorities his papacy, but with the paedophile sex scandals of recent years it is not clear how the Church can re-establish its moral legitimacy and popular appeal.
There are an estimated 1.1 billion Roman Catholics in the world, compared with 1.5 billion Muslims and nearly 600 million Protestants.