The published letter Mundus Novus, in which Amerigo Vespucci recounts his third journey to the New World, is carefully re-examined in this paper to establish its authenticity and veracity. Neither the translator of the letter nor the printer of its first edition can be identified with certainty, but one credible hypothesis is that friar Giovanni Giocondo da Verona was the translator. Analysis of the text shows no deliberate attempt at distortion or deception, only some innocent exaggerations. The author or his translator have been accused of vainglory and even obscenity, but in the context of the period such claims are unfounded and devoid of sense. An examination of the planisphere drawn up by Waldseemüller based on the data brought back by Vespucci reveals important details concerning the Patagonian cordillera and the coastline of central Chile. These details are not mentioned in Mundus Novus because of the policy of secrecy imposed by the rey of Portugal.