Bulgaria, the poorest member of the European Union (EU), became the 21st member of the eurozone on Thursday (January 1), bringing it closer to full European integration. This comes amidst marked political instability and widespread domestic opposition, especially by pro-Russian parties.Bulgaria is retiring the lev, its currency since 1881, which, has been pegged to the Deutschmark and later the euro since 1997.What is the eurozone?The Maastricht Treaty of 1992, which established the European Union, paved the way for:The formation of a common economic and monetary union, which is the European Economic and Monetary UnionThe adoption of a common currency, which would be accepted as the sole legal tender, the euro.A unified central banking system, which established the European Central Bank (ECB).A common economic region.The eurozone, or officially the euro area, refers to the geographic and economic region comprising those members of the EU that have fully adopted the euro as their official currency.Bulgaria’s admission to the eurozone makes it the 21st nation out of 27 EU members to do so. The remaining six use their own currencies instead.Four microstates, Andorra, Monaco, the Vatican City and San Marino, also use the euro through agreements with the EU, while Kosovo and Montenegro use the euro as their sole currency without an agreement. However, none of these countries are not regarded as members of the eurozone.Croatia was the last country to join the eurozone in 2023. Bulgaria’s inclusion increases the population of Europeans using the euro to 350 million.Why join the eurozone?The eurozone offers its members several benefits.Story continues below this adAs the common currency, the euro allows consumers in its member nations to compare prices with other members, boosting competitiveness. The euro also improves the ease of transactions and offers easier access to the markets of fellow member nations.Members enjoy price stability within the region, as the ECB typically targets a 2% inflation rate. The unified monetary policy by the central bank ensures that members can benefit from lower interest rates. As a member, Bulgaria will also get a seat on the ECB’s Governing Council, which sets rates for the eurozone.Membership in the eurozone also eliminates currency exchange costs within the region, and members are insulated from external shocks owing to the sheer size of the eurozone economy. They also enjoy the benefits of a free trade area, which allows the free flow of labour, goods and services, and capital.Bulgaria also stands to gain in other ways. After the US Dollar, the euro is the largest reserve currency, and a vital symbol of European integration and identity. Moreover, the adoption of the euro as the common currency would boost its tourism industry, allowing travellers to move freely through the eurozone without the hassle of converting currency.What makes a country eligible for membership?Story continues below this adAll EU member states – barring Denmark, which has availed an opt-out – are required to join the eurozone, and satisfy certain “convergence criteria”, which ensure that the aspiring member converges with the other members in economic and legal terms.Also Read | Why silver surfed a 160% wave in 2025Effectively, this means that it must be aligned with other EU members in social, economic and political aspects, so that it can operate within the Union’s common market for goods and services, labour and capital. Adopting the euro is seen as another advance towards complete economic integration with other eurozone members. According to the EU, these conditions are meant to ensure that the new member’s economy is prepared for the transition to a single currency and can integrate smoothly into the eurozone area without disrupting the larger eurozone.Candidates for eurozone membership are also expected to make changes to their national laws and rules concerning their monetary policy (national central bank and related issues) to comply with the Treaty.Will Bulgaria adopt the euro immediately?Effective January 1, Bulgarians can make transactions in both the lev and euro, with the euro set to become the only legal tender from February 1.Why is there opposition to Bulgaria’s admission?Story continues below this adOver the past four years, the country has witnessed seven parliamentary elections and widespread corruption, which has eroded trust in the government. In December 2025, former Prime Minister Rosen Zhelyazkov and his cabinet resigned after a wave of country-wide anti-corruption protests. This has resulted in a political split, meaning that Bulgaria’s admission to the eurozone is not the result of a popular consensus.Opinion polls last month showed that citizens remain split over this decision, and there was concern that retailers could take advantage of the confusion to artificially inflate prices. The BBC reported that elaborate consumer protection measures have been implemented, with all shops required to display prices since August 2025.Bulgaria’s cultural and political ties with Russia offer another layer of complication to its admission to the eurozone. Despite Bulgarian membership in both the North Atlantic Treaty Organization (NATO) and the EU – organisations Russia dislikes and sees as a threat to its sovereignty, the two nations are linked culturally through their common Orthodox Christian heritage and the Black Sea.The far-right, pro-Russia Revival Party views Bulgaria’s admission to the eurozone as the country’s road to a potential Greek-style crisis, in which the latter’s economy collapsed and was bailed out thrice amidst severe austerity measures.