The author provides an account of the background to his discovery of bacteriocin production by streptococcal bacteria and the subsequent demonstration over five decades of research that the streptococcal bacteriocin-like activities are distinctive both for the abundance of their production and for the chemical heterogeneity of their structures. The initial impetus for this research was an endeavour to identify candidate bacteriocin-producing, non-disease-associated streptococci for potential development as oral probiotics capable of providing protection to young children against Streptococcus pyogenes infections. The practical outcome of these studies has been the development and commercial distribution of the bacteriocin-producing probiotic strains Streptococcus salivarius K12 (BLIS K12) and S. salivarius M18 (BLIS M18) for application to the control of a wide variety of bacterial infections and disequilibria of the oral microbiota, currently ranging from streptococcal pharyngitis and otitis media to tooth decay and halitosis.