In this paper, the concept of money and monetary mass is defined and the history, round and fundamental functions of money have been processed. The cash mass a mass is both harvested through cash aggregates M1, M2, M3 and M4 related to the liquidity of money. In addition, monetary and policy implemented by the central bank with the aim of regulating the money mass, namely the circulation of money in the country, was also pursued in order to maintain price stability in view of unexpected fluctuations such as inflation and deflation. The Croatian National Bank, the central bank of the Republic of Croatia, in addition to implementing monetary policy, controls the work of other banks and performs tasks such as the creation and exodus of cash, coins and banknotes, i.e. the primary emission of money. All these tasks are laid down in the Constitution of the Republic of Croatia. The achievement of the primary and secondary objectives of monetary policy is implemented by the Croatian National Bank through two types and four monetary policy instruments that are explained individually. All these instruments affect economic growth, increasing employment and improving living standards. As part of monetary policy, which is part of macroeconomic policy, monetarism was defended as a theory of the Nobel laureate, the most famous representative of monetarism Milton Friedman. Finally, a review was made on the current topic "The introduction of the euro in the Republic of Croatia" under which the legal frameworks and deadlines were listed, and an analysis of the possible consequences after the introduction of the euro was carried out, the consequences of which have their advantages and disadvantages. Professional and scientific books and articles and internet sources were used when writing the final paper listed in the literature. The paper is based on a theoretical approach, so no numerical indicators and analyses are presented, assumptions are not presented and hypotheses and research are not used.