There is increasing awareness that the human gut microflora plays a critical role in maintaining host health, both within the gastrointestinal tract and, through the absorption of metabolites, systemically. An optimal gut microflora establishes an efficient barrier to the invasion and colonisation of the gut by pathogenic bacteria, produces a range of metabolic substrates which in turn are utilized by the host (e.g. vitamins and short chain fatty acids) and stimulates the immune system in a non-inflammatory manner. Although little is known about the individual species of bacteria responsible for these beneficial activities, it is generally accepted that the bifidobacteria and lactobacilli constitute important components of the beneficial gut microflora. A number of diet-based microflora management tools have been developed and refined over recent decades including probiotic, prebiotic and synbiotic approaches. Each aims to stimulate numbers and / or activities of the bifidobacteria and lactobacilli within the gut microflora. The aim of this article is to examine how prebiotics are being applied to the improvement of human health and to review the scientific evidence supporting their use.