Public finance is subject to the principle of fairness, which has a vague character and rarely finds an appropriate reflection in law. Supreme Courts and Constitutional Courts of different countries may refer to this principle and disclose the content of fairness in public finance processes. The scope of the article includes legal establishment and realization of the principle of fairness in contemporary Russian tax law. The author investigates this issue mainly considering the Constitutional Court’s legal positions. The Russian Constitutional Court actively refers to the principle of fairness to resolve disputes in taxation. The analysis of Constitutional Court judgements shows that the content of the principle of fairness for tax purposes depends upon a type of public fee. In some cases, the Court uses the principle of fairness in a broader legal meaning and does not interpret fairness for tax purposes using the vaguest terms and words for arguments. In other cases, the Court may use a more specific and narrow meaning of the principle of fairness in cases on imposition of tax and/or tax liability (tax fairness).