Marriage is defined as a union solely between a man and a woman in the constitutions of Armenia, Belarus, Bulgaria, Georgia, Lithuania, Moldova, Poland, Russia, Serbia, Slovakia and Ukraine.

In the 2011 UN General Assembly declaration for LGBT rights, state parties were given a chance to express their support, opposition or abstention on the topic.

[3] Sixteen EU member states condemned the law, calling it a breach of the Charter of Fundamental Rights of the European Union.

Although same-sex relationships were quite common in ancient Greece, Rome and pagan Celtic societies, after Christianity became the official religion of the Roman Empire, severe laws against homosexual behaviour appeared.

This was followed by the Corpus Juris Civilis of Justinian I in 529, which prescribed public castration and execution for all who committed homosexual acts, both active and passive partners.

[9] Forty years after Poland lost its independence in 1795, the sodomy laws of Russia, Prussia, and Austria came into force in the partitioned Polish territory.

Various countries under dictatorships in the 20th century were very anti-homosexual, such as in the Soviet Union, in Nazi Germany and in Spain under Francisco Franco's regime.

[17][18] In 1972, Sweden became the first country in the world to allow people who were transgender by legislation to surgically change their sexual organs and provide free hormone replacement therapy.

[22] Since then, thirteen countries have followed (Lithuania in 1992, Belarus and Moldova in 1994, Ukraine in 1996, Poland in 1997, Latvia and Serbia in 2006, Montenegro in 2007, Hungary in 2012, Croatia in 2013, Slovakia in 2014, Armenia in 2015 and Georgia in 2018).

[38] On 22 October 2009, the assembly of the Church of Sweden, voted strongly in favour of giving its blessing to homosexual couples,[39] including the use of the term marriage, ("matrimony").

Under the Danish marriage law, ministers can refuse to carry out a same-sex ceremony, but the local bishop must arrange a replacement for their church building.

On 22 May 2015, Irish citizens voted on whether to add the following amendment to the constitution: "Marriage may be contracted in accordance with law by two persons without distinction as to their sex".

62.1% of the electorate voted in favour of the amendment, making Ireland the first country worldwide to introduce same-sex marriage through a national referendum.

[53] On 1 January 2012, a new constitution of Hungary enacted by the government of Viktor Orbán, leader of the ruling Fidesz party, came into effect, restricting marriage to opposite-sex couples and containing no guarantees of protection from discrimination on account of sexual orientation.

[54] In 2012, the United Kingdom government launched a public same-sex marriage consultation,[55] intending to change the laws applying to England and Wales.

On 4 February 2014, the Scottish Parliament passed a bill to legalise same-sex marriages in Scotland as well as ending the "spousal veto" that would allow spouses to deny transgender partners the ability to change their legal gender.

[57] On 30 June 2013, Vladimir Putin, President of Russia, signed the Russian LGBT propaganda law into force, which was approved by the State Duma.

[59] On 14 April 2014, the Parliament of Malta voted in favour of the Civil Union Act which recognises same-sex couples and permits them to adopt children.

On the same day the Maltese parliament also voted in favour of a constitutional amendment to ban discrimination based on sexual orientation and gender identity.

[66] And on 18 March 2016, the Government introduced a bill to allow legal gender change without any form of psychiatric or psychological evaluation, diagnosis or any kind of medical intervention, by people aged at least 16.

[78] On 9 January, the parliamentary committee on constitutional issues approved a series of amendments, including the aforementioned limitation of marriage and the additional requirement of a two-thirds majority for any future regulation of marriage, family and civil unions (a requirement previously reserved only for issues such as sovereignty and territorial questions).

This final parliamentary session was commenced on 26 January but never concluded, as the ruling coalition did not obtain the two-thirds majority required.

[98][99] In October 2017, the Parliamentary Assembly of the Council of Europe adopted the first intersex-specific resolution of its kind from a European intergovernmental institution, after 33 members voted in favour.

[117] According to pollster Gallup Europe in 2003, women, younger generations, and the highly educated are more likely to support same-sex marriage and adoption rights for gay people than other demographics.

[118] A Eurobarometer in 2006 surveying up to 30,000 people from each European Union country, showed split opinion around the then 27 member states on the issue of same-sex marriage.

All other countries within the EU had below 50% support; with Romania (11%), Latvia (12%), Cyprus (14%), Bulgaria (15%), Greece (15%), Lithuania (17%), Poland (17%), Hungary (18%) and Malta (18%) at the other end of the list.

[128] In Croatia, a poll from November 2013 revealed that 59% of Croats think that marriage should be constitutionally defined as a union between a man and a woman, while 31% do not agree with the idea.

[130] Public support for same-sex marriage from EU member states as measured from a 2015 poll is the greatest in the Netherlands (91%), Sweden (90%), Denmark (87%), Spain (84%), Ireland (80%), Belgium (77%), Luxembourg (75%), the United Kingdom (71%) and France (71%).

[142] In Croatia, a poll conducted in November 2013 revealed that 59% of Croats think that marriage should be constitutionally defined as a union between a man and a woman, while 31% do not agree with the idea.

[131] A 2015 NDI public opinion poll shows that only 10% of the population in the Balkans (Serbia, Bosnia and Herzegovina, Albania, Kosovo, Montenegro and North Macedonia) believe LGBTI marriages are acceptable, in contrast to 88% who think they're unacceptable.