The term post-truth is a neologism to describe a situation that, at the time of creating and modeling public opinion, makes objective facts have less influence than invocations to emotions and personal beliefs. In fact, the Oxford English Dictionary chose this term as the word of the year 2016. Many publishers say they have observed an increase of two thousand percent in the use of the term in written media. They attribute the increase to the referendum on Brexit, in Great Britain, and to the presidential election process that gave Trump the victory in the United States. For many people, the post-truth is lie, falsehood or hidden gyp. It is also a concept that can disguise the traditional political propaganda and the use of public relations and strategic communication as instruments of manipulation and propaganda. These situations, by the way, have accompanied us for centuries. However, at the present post-truth acquires notoriety since the propaganda fictions acquire more value. We prefer to create myths before analyzing objectively. In addition, prejudice and irrational diatribe have subordinated objective argumentation. As a result, the underlying problem is that this post-truth touches the spheres of political power, but it also manifests itself in other structures, institutions, conditions and social and cultural groups: work, ethics, education, business, the family, the media, religions, among others. This will take precedence about how to base and assess facts in society and the world in general.