Penicillin was the first broad-spectrum antibiotic. It revolutionized the treatment of infectious diseases, and became an instrument of mass medical care in the aftermath of World War II. Deep-fermentation methods, which had been developed for the production of penicillin during the war, gave rise to the antibiotics industry, and contributed to the new biotechnology industry which appeared in the 1970s. For all these reasons, penicillin had a major impact on the second half of the twentieth century.