Throughout history, countries have established monetary unions as a way to achieve economic goals through integration. When entering integration, countries have different options and levels of integration to choose from, such as removing trade restrictions, creating a customs union, or harmonizing different policies. Economic and monetary union represents a special form of integration where countries use the same currency and implement a common monetary policy through a common central bank. It is the highest form of economic integration, and the European Union (EU) is an example of such a union that strives to achieve common goals. The euro, as the single currency of the European Union, symbolizes the possibilities that the EU provides by uniting and connecting European countries. It facilitates trade and financial transactions within the Eurozone and promotes economic integration among the countries that use it. The euro is considered a symbol of European unity and stability, although it faces challenges such as economic coordination and maintaining stability over time. This paper aims to analyze the advantages and disadvantages of monetary unions, their characteristics and criteria for maximum realization of economic benefits. The research focuses on the progress in the establishment of monetary unions and the criteria for joining them. The purpose of the paper is to present the preconditions for joining the European monetary union. The preconditions ensure that the eurozone member state maintains economic stability and adheres to common standards to ensure a successful introduction of the euro. The paper examines the potential costs and benefits of entering the mentioned union for both citizens and the economy, and whether they bring more benefits or disadvantages. The main idea of this work is the analysis of the public opinion of citizens on the advantages and disadvantages of the Republic of Croatia's entry into the eurozone and the euro. The aim of the work is to analyze the key characteristics of the common supranational currencies dollar and euro and how they are used in monetary unions. The implementation and acceptance of the euro in Croatia as the 20th member of the eurozone will be examined in this paper in the practical part of the study, comparing the data of the Croatian National Bank with the results of our own research on the perception of the citizens of the Republic of Croatia about the introduction of the euro in 2022.