This paper aims to show the importance of the function assumed by trust in the present society, and to provide an overview of the main interaction patterns between trust and private law. We shall start by trying to give a definition of trust according to the socio-cognitive theory. Then we shall examine the most important private law principles involved with both trust and reliance, such as good faith, and shall particularly focus on the so-called appearance principle and its main applications by jurisprudence and doctrine¹.