Bacterial interactions, antagonistic and synergistic, help maintain the balance in the normal endogenous flora. The production of bacteriocins by microorganisms is one of the important mechanisms used for interference. The ability of various microorganisms to produce bacteriocins and exhibit interfering capability is detailed in the review. These organisms include Gram-positive and Gram-negative aerobic and anaerobic bacteria. The role of bacterial interference (BI) in clinical infections and the effect of this phenomenon on their eradication is detailed. The infections discussed include those of the upper respiratory (pharyngo-tonsillitis, otitis media), urogenital, and gastrointestinal tracts. The influence of antimicrobial agents on these organisms and their interactions with other bacteria are also described.