Faustino Ballvé was a remarkable thinker and economist, educated in Spain and England and teaching and practicing law in Mexico City. He was here when Ludwig von Mises came to speak on a lecture tour. The talks that Ballvé heard sparked a new intellectual energy in him. He carried on a long correspondence with Mises himself, checking his education from graduate school against Mises's views. They became good friends. The result of his studies and correspondence was this splendid book, which really ought to be considered a classic. It was published first in 1956, and had a massive impact in Latin America. It was translated and published in English in 1965, and went into many other foreign translations. The language is elegant and principles enduring. Its popularity was due in part to its brevity combined with its scope: at only 129 pages, it covers nearly the field of economics.