In this teaching note I explain a method to obtain consensus among the members of a group. This method is the well known Delphi Method. This method is useful to close the gap between the total ignorance regarding a fact or situation and a disciplined guess. I present the origin of the name, that is associated to the Delphos Oracle in Greece and I define the origin and operational procedure as well. I mention the advantages, the basic elements and the most common critiques and objections found in the literature. Finally, I present the most common uses of the method. In the last section I conclude. This note is not intended to present something really new. It is just an actualized bibliographic review.