The global financial and economic crisis has forced many countries to mobilize significant amounts of public funds to rehabilitate and rescue financial institutions, leading to the European Union's consensus to impose an obligation on the financial system to participate more in public finances. One of the areas that requires reform moves is certainly the taxation of the financial sector, and taxes on financial transactions and taxes on capital gains stand out as two important methods. Their goal is to discourage risky behavior in the financial sector and ensure that the financial industry takes greater responsibility and cost of the current financial crisis. The specialist diploma thesis "Taxation of capital gains and financial transactions in Croatia and European Union countries" will use literature in the field of (taxation) of financial transactions, the functioning of financial systems, the structure and organization of the payment system and taxation of capital income and capital gains, surtax on income tax and tax treatment of interest on deposits, namely: books, professional and scientific articles, official statistical reports, financial planning documents, laws and Internet sources. The paper presents a systematic overview of the knowledge on the tax on financial transactions and capital gains, their practical application in the countries of the European Union and the Republic of Croatia and their effects on financial markets. Keywords: financial sector taxation, financial transaction tax, capital gains tax, financial market impact