Streptomyces spp. are common soil-borne microorganisms that are noted for their abilities to produce antibiotics and other secondary metabolites. About two-thirds of the naturally occurring antibiotics are produced by Streptomyces spp. and other actinomycetes. This chapter presents the systems in which streptomycetes have been investigated for their ability to act as biocontrol agents. It aims to summarize the information obtained in the programs on the use of Streptomyces spp. for the biological control of potato scab. Common scab of potato is caused primarily by Streptomyces scabies, although other species of Streptomyces have been reported to cause potato scab. Effects of NPK fertilizers on potato scab incidence are not conclusive since some studies have suggested that the fertilizers decreased the disease in potato while others have indicated that the fertilizers did not affect disease incidence. Naturally occurring disease-suppressive soils have been investigated for a number of pathogen-host systems.