This book presents very important knowledge about antibiotics, their definitions, their origins and their classification as well. A detailed study was given about actinomycetes, especially the antibiotic makers, streptomycetes, their discovery and their ecology. The author described best methods used for actinomycetes isolation from natural sources and highlighted the role of Streptomyces species and gave a very significant and rapid way to differentiate between the very similar strains, which is, Randomly Amplified Polymorphic DNA (RAPD) analysis, in addition to 16S rRNA gene sequence. Optimum condition for maximum antibiotic production by actinomycetes isolated from Iraqi and Egypt soils was also studied using two different ways, a one-factor-at-a-time approach and statistical experiment design. Extraction and purification of bioactive molecules produced by these microorganisms were also carried out in the University of Warwick,UK. Thus, we can say that this book takes researchers and students up to a level from which they can approach real understanding in this field and encourage their attempt to find out clinically useful antibiotics or screen out new potent actinomycetes.