Bulgaria and Romania officially signed the Treaty of Accession in Luxembourg, which allowed their entry into the European Union as member states. The signing ceremony was attended by key EU officials, including the then-President of the European Commission, José Manuel Barroso. This historic occasion capped a lengthy period of negotiations that began after both countries applied for EU membership in the early 2000s. Bulgaria and Romania have made extensive reforms to meet the EU's Copenhagen criteria, which include political stability, functioning market economies, and the adoption of EU laws and standards.

The treaty signing symbolized a major Geopolitical shift in Southeastern Europe, indicating a commitment to democratic governance and economic integration with Western Europe. This move also reflected the EU's continued expansion and integration efforts in response to the end of the Cold War and the desire to promote stability and prosperity in the region. The accession was seen not only as a celebration of European unity but also as a way for Bulgaria and Romania to strengthen their political and economic ties with their European neighbors.

Bulgaria and Romania officially became EU members on January 1, 2007. Their integration into the Union set a precedent for other countries in the Balkans striving for similar membership, highlighting the EU's role as a stabilizing factor in the region. The benefits of EU membership for both countries included access to EU funding, increased trade, and the ability to participate in European policymaking.