Organic acids are naturally-occurring, carbon containing compounds with acidic properties. Organic acids have antimicrobial activity, which has been utilised for centuries to control undesirable microorganisms in foodstuffs. Interest in the use of organic acids for farmed animals has increased primarily as a result of the desire to reduce foodborne pathogens and the decreasing global acceptance of the use of antibiotics as growth promoters (AGPs). Whilst acidity (or pH) has a profound effect on microbes, it is the undissociated portion of an organic acid that is believed to contribute significantly to their antimicrobial effect. This review focuses on the microorganism, its ability to tolerate acid stress, the effect of organic acids and considers key work behind the application of organic acids in the global poultry industry. This application focussed initially on controlling Salmonella in the feed and intestine of poultry. More recent work with organic acids has highlighted the apparent wider benefits to poultry intestinal health, from improvements in gut morphology to regulation of bacterial virulence gene expression, which are outlined in this review.