Principle of tax fairness belongs to social-political principles of financial theory. Its application in tax systems of modern countries should ensure a uniform taxation “between the equals” and a redistribution of income and wealth “between the unequals”. The horizontal tax fairness implies that the “equals should be taxed equally”, meaning that the individuals with the same economic force (income, revenue, property) should contribute in equal way to the state for public goods and services received in return. The vertical tax fairness is ensured in a way that individuals are taxed in accordance with their economic force, meaning that the better off should pay higher taxes. Globalisation of financial and economic flows has caused a transformation of principle of tax fairness from national principle necessary for designing a fair national tax system into a global concept of fair taxation, that should ensure a fair distribution of tax burden between countries.