(Title in Polish - 'Zasady: dobrej wiary i uczciwego obrotu oraz swobody umów w kodeksie zobowiazan oraz Zasadach Europejskiego Prawa Umów'). The publication is devoted to the two of key principles in modern civil law studies: principle of good faith and fair dealing as well as the principle of freedom of contract. The presentation of those principles in light of two acts of law that vary in nature and time of creation allows for demonstrating how permanent they are and how essential to the civil law of the countries with free market economy. The two discussed principles have been present both in the code of obligations and in the Principles of European Contract Law (PECL). Their role in both acts was important and similar, though the code of obligations attached relatively smallest importance to the fair dealing principles clause. As concerns the principle of freedom of contract, the PECL have repeated the solution, the forerunners of which were, among others, the authors of the code of obligations, namely the regulation of the principles of freedom of contract with a positive approach. The principles of good faith (in case of the PECL - also the principles of fair dealing) are visible, both under the code of obligations and the PECL, in the entire duration of the obligation relationship between the parties, starting from the moment when the parties express their intentions to the interpretation of the statements of intent (contracts) to the performance of obligations (contractual obligations). The conducted analysis of the code of obligations and the PECL allowed the author to bring up several theses of vital importance to the idea of trans-national unification of private law and for the history of Polish law, which can be summed up in form of the following conclusions: 1. the principles lying at the foundations of the PECL have been present in the Polish law for at least several dozen years; 2.the principles of freedom of contract as well as good faith and fair dealing, particularly important to the modern civil law studies, have played an important role in the Polish pre-war legislation as well; 3. certain solutions, relatively innovative at the time when the code of obligations was adopted, subsequently found their regular place in the European civil law.