Antibiotic research from the discovery of Fleming to our days has been a fascinating, exciting, continuously changing, and developing adventure. As a result of the frenzied research of the past 50+ years, in our days, tens of thousands of natural products derived from microbial sources are known. Interest in the eld has been generally increasing, although sometimes there has been decline; interest and the whole story shows some cyclic features with successes and failures and evolved around changing clinical needs and new enabling technology. After the revolution in the “heroic” or “golden” era, in the 1940s and early 1950s, when almost all groups of important antibacterial antibiotics (tetracyclines, cephalosporins, aminoglycosides, and macrolides) were discovered, the success story continued. It seemed in the 1950s and 1960s that the main problems of chemotherapy had been solved. Antibiotics discovered in this period were mainly isolated from Streptomyces species, representing approximately 70-80% of all the isolated compounds. They were primarily active against bacteria and fungi. In this period, the discovery of antitumor, antiviral, and nonantibiotic-enzyme inhibitory-metabolites had just started (Bérdy 1985).