The first two decades of the 20th century witnessed the introduction and expansion of reinforced concrete as a building material in Spain. Few years passed between the introduction of the first patents in the most industrialized areas of the Iberian Peninsula and the subsequent generalization of the technique through scientific knowledge obtained in universities. This period coincides almost completely with the professional career of Antoni Gaudí, one of the most famous Catalan architects. This study reports that Gaudí had contact with this new material and discusses the transition he made from the traditional construction methods to the use of reinforced concrete in his later works. Placing the starting point in the relationship between Antonio Gaudí and the industrialists who built the first cement factories in Catalonia (especially Eusebi Güell), the research on the patents to which he had access are presented and the characteristics of his works with reinforced structures and materials are described.