The study that is presented for consideration of the reader tries to go into depth in the Good Faith Principle, in its most general aspects to later derive the analysis to which has been named “con- tractual good faith”, due to the particular field in which it acts. In relation to the latter, which fulfills important functions in all the obligations and contracts law, the function stands out in which it carries out in the integration of the contractual contents, particularly as to, due to the silence of the parties, the good faith includes in the program of rights and duties derived from the contract, all those that rise from the nature itself of the relation or those who turn out as ordinary in the regulation of the typical figure dealt about (articles 1603 of Civil Code and 871 of the Commerce Code). Finally, in the study a recount is done about the origin and the most outstanding manifestations of those that have been named “secondary conduct rights”, which constitute one of the most important and daily expressions of the integration effect that the good faith has with respect to the contractual contents.