In this lecture Professor Saladino (University of Tuscia, Viterbo - Italy) states that prebiotic chemistry plays a central role in the investigation of the possible scenarios of the early chemical environments. Its goal is to shed light on the events involved in the synthesis of initial biomolecules and on the self-organization processes that led the last common ancestor. Even though a well defined scenario for the physico-chemical conditions on the primitive Earth is not available, one can assume that a synthetic pathway, in order to be considered prebiotic, should use the simplest chemicals and the most common conditions present at that time.