Flavor development in bacterial-ripened cheese requires metabolism of milk components by lactic acid bacteria (LAB). The microorganisms that contribute to these reactions include LAB that are deliberately added to milk (e.g., starters or adjunct cultures) as well as nonstarter LAB (NSLAB), which are usually lactobacilli, that enter cheese through the processing environment. Research indicates that different NSLAB strains can exert a positive, neutral, or negative effect on cheese flavor development, and some isolates have been shown to promote cheese quality defects. Because they cannot be readily controlled, the complex and dynamic nature of ‘wild’ NSLAB communities is viewed as a major source of cheese flavor inconsistencies and random defects. Thus, efforts by the dairy industry to consistently produce uniform, high-quality cheese will ultimately require technology to control the composition and growth of NSLAB communities during cheese ripening. Although Lactobacillus adjuncts hold promise as a tool for this purpose, effective realization of this technology will require a more fundamental understanding of the factors that determine which species or strains will proliferate in ripening cheese. Fortunately, recent advances in genomics and other molecular biology techniques are now providing researchers with the sophisticated tools they need to realize this goal.