The last two decades have seen a substantial increase in the use of aromatic herbs and essential oils as feed additives in animal nutrition. One of the main reasons for this trend is to substitute antibiotic growth promoters, which have been completely banned as feed additives in the European Union since 2006 because they are suspected of contributing substantially to increasing resistance among human pathogens. Recent investigations have shown significant antimicrobial effects of several essential oils and essential oil compounds against enteropathogenic organisms in farm animals. Porcine proliferative enteropathy caused by specific Escherichia coli strains could be controlled by in-feed application of carvacrol-rich essential oils, and the effect of some essential oil components against Clostridium perfringens and necrotic enteritis was confirmed in poultry. In ruminants, an improvement of the digestion was observed, resulting in reduced methanogenesis and nitrogen excretion. In addition, the antioxidative activity of aromatic plants and essential oil compounds contributes to the stability and palatability of animal feed and has, moreover, resulted in an improved shelf-life and quality of animal products, due to reduced oxidation. The 'growth-promoting effect' of essential oils (feed conversion rate, daily weight gain, etc.) is not as evident, since a large number of publications are (commercial) product-driven, lacking data on the starting material. Nonetheless, the overall efficacy of essential oils and aromatic herbs, especially their non-nutritive value with impact on the health status and benefit of animals and humans (via the food chain), is encouraging further research and development in this field. Copyright (C) 2009 John Wiley & Sons, Ltd.