Treaty of Trianon, an international document of unquestionable political-legal value and, at the same time, of capital value for Romania, which certifies the full legitimacy of its existence inside its current borders - also including Transylvania -, is unconditionally fully valid and thus remains as such, having been applied for a century. It is for the Romanians to comply with the sacred duty to know its provisions as rigorously as possible and to ensure, at any cost and without any hesitation, the strict observance of its provisions. Under no circumstance it is admitted a hesitating or passive attitude, without reply when its validity is questioned. Thus, it is created the impression that Romania would agree that the Treaty of Trianon is no longer of interest to the Romanian State or that there would be some indifference to the regulations which it contains, favouring confusions and forming opinions that prejudice the value of this Treaty. This study presents the context in which the Treaty of Trianon was negotiated and reached the signing; the Paris Peace Conference (1918-1920) is described and the principles underlying it and the decisions adopted are mentioned. Similarly, the author makes a characterization of the treaties signed after the end of the First World War and it is mentioned that the principle of nationalities was laid at the foundation of the new order in Europe. The Paris Peace Conference put an end to the oppressive empires, and the liberated nations were constituted in sovereign national states, and, as the case may be, new states emerged, while others were reformed or reunited - this being also the case of the achievement of Greater Romania. In the final part of the study, it is described the series of irredentist attempts started since the Paris Peace Conference (1918-1920) and continued throughout the entire century, to revise or even repeal the Treaty of Trianon. The most brutal action in this regard was the Vienna Arbitration (30 August 1940), which fortunately was annulled by the Paris Peace Treaty (1947), which declared it null and void. The Treaty of Understanding, Cooperation and Good Neighbourliness between Romania and the Hungarian Republic (1996) - necessary, of course, and useful insofar as it would be applied in good faith by both parties - contains nevertheless a series of extreme concessions granted by the Romanian side, that a kind of condominium has been created in the area where a population of Hungarian ethnicity is located next to Romanians. It is especially surprising that, although there is a provision regarding the intangibility of the borders, in the Treaty of 1996 it is not mentioned the Treaty of Trianon under which they are established, which raises many questions. The author does not overlook that, given that the Romanian citizens of Transylvania - Hungarian or even Romanian - are granted Hungarian citizenship, an attempt is made to extend the jurisdiction of Hungary on the territory of Romania, and the massive acquisition of property in Transylvania by Hungarian citizens aims to create a situation favourable for Hungary and to the detriment of Romania. [ABSTRACT FROM AUTHOR]