The article contains the characteristics of the Concordat between the Holy See and the Republic of Poland (1993-1998). First, the Author pays attention to the religious and political ties between Poland and the Holy See at the time of the Christianity of the first historical Polish ruler, Mieszko I (966) who gave his state under the protection of the Holy See. He wanted to protect Poland from Sacrum Imperium Romanum Germanorum. Then, the Author presents the significant meaning of the Concordat between the Holy See and the Republic of Poland concluded at the time of the political transformations from the totalitarianism to the democracy and at the same time from the atheistic regime of the communist state with hostile separation to the democratic state with friendly separation. The article discusses the following issues: the notion and classification of concordat agreements, the legitimization of the concordat in axiological and formal aspects based on the Constitution of the Republic of Poland of 1997, the range of the concordat’s regulations, the effectiveness of the concordat in domestic legal order.