Biological control is the suppression of damaging activities of one organism by one or more other organisms. They are many environmental benefits of biological control including safety for humans and other non-target organisms, reduction of pesticide residues in food, increased activity of most other natural enemies, and increased biodiversity in managed ecosystems, their advantages are numerous. microorganism–microorganism or microorganism–host interactions involve all ecological aspects, including physiochemical changes, metabolite exchange, metabolite conversion, signaling, chemotaxis and genetic exchange resulting in genotype selection. Microbial interactions occur by the transference of molecular and genetic information, and many mechanisms can be involved in this exchange, such as secondary metabolites, siderophores, quorum sensing system, bio-film formation, and cellular transduction signaling, among others. The agricultural importance of the biocontrol is that possess good antagonistic abilities against plant pathogenic microbes. Antagonism is based on different mechanisms, like the production of antifungal metabolites, competition for space and nutrients and myco-parasitism. Some of microbes like Trichoderma strains with effective antagonistic abilities are potential candidates for the biological control of plant diseases. Biotic and biotic environmental parameters may have negative influence on the bio-control efficacy of biocontrol strains.