The functioning of modern states cannot be conceived without taxation. However, there are huge differences from one country to another in terms of the degree of taxation of the economy and the structure of taxes that bring revenues to the budgets of public authorities. Our article makes an analysis of the literature on optimal taxation. Ideas on the progressiveness of income tax, flat taxation of capital gains, ways of taxing property, different taxation of certain categories of goods and services, etc. are reviewed. The empirical study on OECD countries identifies some correlations between five categories of taxes and several socio-economic characteristics: gross domestic product, unemployment rate, population density, stock market capitalization of companies and the intensity of goods movement. Using hierarchical clustering, we highlight the existence within the OECD of five relatively homogeneous groups of countries regarding the structure of taxation. The categories of taxes analysed are total collected revenues, personal income tax, corporate profit taxation, mandatory social contributions, property taxes and taxes on goods and services.