In August 1900, during the Second International Congress of Mathematicians, held in Paris, David Hilbert proposed 23 problems, well known since then. He tried to anticipate and, up to a certain point, to determine the subjects and predictable development of mathematics for the new century beginning. According to his opinion the vitality of a science in a given epoch depends directly on the number of problems raised, since they constitute the guide which directs the efforts of scientists.