The First Agreement of Principles Governing the Normalisation of Relations, informally known as the Brussels Agreement (Serbian: Бриселски споразум / Briselski sporazum, Albanian: Marrëveshja e Brukselit), is an agreement to normalize relations between the governments of Serbia and Kosovo. The agreement, negotiated and concluded in Brussels under the auspices of the European Union, was signed on 19 April 2013. Negotiations were led by Serbian prime minister Ivica Dačić and Kosovo prime minister Hashim Thaçi, mediated by EU High Representative Catherine Ashton. The government of Serbia does not recognise Kosovo as a sovereign state, but began normalising relations with the government of Kosovo as a result of the agreement. In Belgrade, the agreement was criticized by protestors as a convalidation of Kosovo independence.

Following the Kosovo War and the NATO bombing of Yugoslavia in 1999, Kosovo (as part of Serbia and the Federal Republic of Yugoslavia) was placed under United Nations administration under UNSC Resolution 1244. Kosovo unilaterally declared independence in 2008, which has been recognised by 110 countries. However, Serbia maintains that Kosovo continues to be part of its territory. European Union-mediated dialogue between Kosovo and Serbia began in March 2011. Serbia and Kosovo were urged to continue talks in Brussels, but Serbia was not obliged to recognise Kosovo during the process.

Ten rounds of talks were held at the European External Action Service office in Brussels. EU High Representative Catherine Ashton chaired the talks for two years, followed by Federica Mogherini. Normalisation of relations with neighbouring states is a key precondition for states wishing to join the EU; the Brussels Agreement brought Serbia close to EU accession talks and Kosovo to initializing a Stabilisation and Association Agreement (SAA). The SAA was signed by HR Mogherini and Kosovar prime minister Isa Mustafa in October 2015.

United States diplomats have supported the EU-led dialogue. U.S. secretary of state Hillary Clinton invited Baroness Ashton to travel in the Balkans, and they made joint visits to Belgrade, Pristina, and Sarajevo in October 2012.

The European Commission advised beginning an SAA with Kosovo after the agreement was concluded, and accession negotiations began with Serbia. The agreement was supported by the European Union, NATO, the OSCE, and the United Nations.

The two-page agreement has 15 paragraphs. Paragraphs 1–6 concern the establishment, scope, and functions of the planned Community of Serb Municipalities. Paragraphs 7–9 concern police and security, specifying one police force for all of Kosovo (including the north) known as the Kosovo Police. Paragraph 11 stipulates that municipal elections shall be held throughout Kosovo under Kosovo law. Paragraph 12 provides for the creation of an implementation plan and specifies a date (now past) by which the plan would be concluded. Paragraph 13 undertakes to intensify discussions on energy and telecommunications. According to Paragraph 14, "Neither side will block, or encourage others to block, the other side's progress in their respective EU paths." Paragraph 15 envisages the establishment of an implementation committee with EU facilitation.

The document agrees on the integration of Serb-majority municipalities in North Kosovo into the Kosovar legal system, with two guarantees:

After the agreement was signed, meetings have been held regularly to implement its provisions. A judicial agreement was reached in February 2015, followed by agreements on energy and telecommunications operators. On 25 August of that year, an agreement was concluded to establish the Association of Serbian Communities.