Protestantism in Luxembourg
The practice of Protestantism in Luxembourg is divided across several different churches and denominations. The largest Protestant churches in the Grand Duchy are the Protestant Church of Luxembourg, Protestant Reformed Church of Luxembourg, Evangelical Church in Germany, Church of England, and Protestant Church in the Netherlands. Altogether, Protestantism is the largest minority religion in Luxembourg (after the majority Roman Catholic Church), with estimates of adherents ranging from 5,000 to 15,000 (1% to 3.2% of the population).
As a result of fierce opposition by Jesuit counter-Reformationists, Protestantism was outlawed in Luxembourg until 1768. By 1815, Luxembourg had small populations of Lutherans, Calvinists, and Waldensians. The Congress of Vienna changed the religious establishment; not only did Luxembourg pass to the Protestant House of Orange-Nassau, but it was also occupied by the armies of Protestant Prussia. The first permanent Protestant church was Luxembourg City's Baroque Trinity Church, which was appropriated by the Prussian garrison to hold their services. When the Prussian army left Luxembourg, the Trinity Church passed to the civilian population.
Most of the nineteenth century saw little change in the religious composition of Luxembourg's population, with only a marginal increase in the number of Protestants. However, towards the end, tens of thousands of German immigrants, many of whom were Lutheran or Calvinist, moved to Luxembourg to work in the steel industry. Grand Duke Adolphe sought to both recognise the contribution of Protestants and to establish state authority over the new denominations. To these ends, he ordered the creation of a new church, the Protestant Church of Luxembourg (PKL), which would unite the Lutherans and Calvinists together. Immediately, new church became recognised by the state as an officially-mandated religion, similar in status to the Roman Catholic Church.
Nonetheless, generally, Protestants did not join the new church. The Grand Ducal decree that established the PKL described its theology as "of the Augsburg and Helvetian creeds", meaning a synthesis of Lutheranism and Calvinism. This alienated the new immigrants, who were unwilling to change their religious beliefs to conform, and the separate creeds survived. In recognition of the failure to unite the churches, in 1982, the state created the Protestant Reformed Church of Luxembourg (PRKL), a Calvinist church based in Esch-sur-Alzette.
Throughout the twentieth century, the growth of expatriates in Luxembourg caused a surge in number of foreign Protestant churches. New churches includes Lutheran churches from the Netherlands, Denmark, and Sweden, Anglican and Presbyterian churches from the United Kingdom, and Evangelical churches from the United States. In 2003, the Church of England unsuccessfully applied to be given the same officially-mandated status as the PKL and the PRKL. 
- International Religious Freedom Report 2004 - Luxembourg. 8 November 2005. US Department of State. URL accessed 12 May 2006.