This paper focuses on two questions: What made the Treaty between the Polish People’s Republic and the Federal Republic of Germany Concerning the Basis for Normalizing Their Mutual Relations concluded half a century ago in Warsaw (December 7, 1970) particularly significant among many other treaties? How did a state with limited sovereignty, such as Polish People’s Republic at that time, managed to negotiate an agreement to defend its sovereignty, territorial integrity and inviolability of its borders? The essay refers to the works of outstanding Polish researchers from the “Poznań school” of international law (Alfons Klafkowski, Krzysztof Skubiszewski, and Bolesław Wiewióra) as well as Manfred Lachs, Ludwik Gelberg and other researchers of the subject, in particular to the original thoughts of Janusz Symonides on the principle of effectiveness in international law. Rather than providing an exegesis of the text of the Treaty, this study analyses the political context and explanation of subtexts which only came to light years later. Difficulties in negotiating the agreement were related to the so-called German question. The Polish side called for unequivocal recognition of its western border, while the Federal Republic of Germany sought to conclude a Treaty on the nonuse of force (Gewaitverzicht). An additional difficulty was the negative attitude towards the Polish initiative on the part of the ‘allied’ German Democratic Republic neighbouring with Poland. Its leaders believed that Polish postulates to recognize the border on the Oder and Neisse line undermined the permanent nature of the statehood of “the first state of workers and peasants on German soil.” In addition, Poland’s eastern neighbour, the USSR, was interested in concluding a treaty with the Federal Republic of Germany, which would guarantee the inviolability of the Polish western border, and thus these guarantees would perpetuate the legal legitimacy of Poland’s dependence on the USSR sphere. In these circumstances, the bilateral agreement reached had existential significance for Poland. It also paved the way to launching the process leading to conclusion of the Helsinki Final Act during the Conference on Security and Cooperation in Europe (1975). The main causative factor was the political will and determination of both architects of this Treaty – Władysław Gomułka and Willy Brandt, who was awarded the Nobel Peace Prize for restoring moral values in politics.