On June 30, 2005, Spain became the third country in the world to legalize same-sex marriage when a law passed by the Cortes Generales took effect. The vote in Congress had passed decisively in July 2004, but the June 2005 implementation date marked the moment Spanish couples could legally marry regardless of gender. Spain joined only the Netherlands (2001) and Belgium (2003) as nations recognizing same-gender marriage, positioning the country among global pioneers on LGBTQ+ rights.

The Spanish law granted same-sex couples full marriage rights equivalent to heterosexual couples, including adoption privileges and inheritance protections. Prime Minister José Luis Rodríguez Zapatero championed the measure despite significant opposition from the Spanish Catholic Church and conservative political parties. The Socialist government framed marriage equality as a matter of fundamental dignity and constitutional rights. On the first day the law took effect, Spanish couples lined up at civil registries across the country to marry, with ceremonies celebrated in Madrid and other major cities. International media coverage highlighted Spain's progressive stance on LGBTQ+ issues during a period when most of Europe and the Americas still restricted marriage to heterosexual couples.

The law proved transformative for Spanish society and demonstrated that same-sex marriage could be implemented smoothly without the social upheaval opponents predicted. Spain's decision influenced debates across Europe and Latin America, contributing to a cascade of legalization efforts over the following decades. By 2026, 38 countries would recognize same-sex marriage, serving populations totaling 1.5 billion people. Spain's 2005 action, arriving just decades after Franco's repressive dictatorship, symbolized the nation's evolution toward modern democratic values and social inclusion, establishing a legal and cultural foundation that continues defining Spanish identity today.