The theme of this graduate thesis refers to the application of the clause rebus sic stantibus, ie the institute of modification or termination of the contract due to changed circumstances. This paper has been elaborated through several interrelated thematic units that are arranged chronologically. In the introduction and the second unit, the concept of changed circumstances and the need to apply the institute of changed circumstances is approximated. The Institute is now accepted in foreign legislation and legal practice. Foreign jurisdictions have had a strong influence throughout history on development of the Croatian contractual law and the development of the institute of changed circumstances (clause rebus sic stantibus). A review on the past of the clause is described in order to find out the path to the results of long-lasting evolution and maturity, through various oppositions and struggles on the philosophical but legal field through which it is seen that law has its own development path and logic of development, developing a unique legal institute such as an institute of changed circumstances, a clause rebus sic stantibus, in various environments and ages, under different influences. The institute of changed circumstances, ie the clauses of rebus sic stantibus, in positive Croatian law, constitute provisions that regulate the legal consequences of such situations that would have been neglected by the consistent application of an absolute obligation to alter the circumstances of the affected party, thereby preventing adaptation to newly emerging circumstances, which is dealt with through the following units. The Institute of changed circumstances exists in Croatian civil law as a natural constituent of bilateral contracts since entering into force of the new Civil Obligations Act 1978, before which it was regulated in the commercial law for General Terms for Trade of Commodities. By entering into force of the new Civil Obligations Act on 2006, the rebus sic stantibus clause is being reformed. Furthermore, the requirements that must be met in order to achieve the right to change or terminate and also, case law and case law solutions outlining the application of the clause rebus sic stantibus as a general rule are provided and can be used when interpreting and applying the provisions. At the end of this paper, it is possible to raise the situation where it is impossible or very difficult for one side to fulfill its contractual performance and in international trade operations where the unifying provisions of the Vienna Convention are of the utmost importance. In the conclusion, a review of the entire graduate thesis and the most important facts that are more elaborated in the work are presented, which clarify the need for the generally accepted clause rebus sic stantibus.