Summary Resistant starch (RS) refers to the portion of starch and starch products that resist digestion as they pass through the gastrointestinal tract. RS is an extremely broad and diverse range of materials and a number of different types exist (RS1–4). At present, these are mostly defined according to physical and chemical characteristics. RS may be categorised as a type of dietary fibre, as defined by the American Association of Cereal Chemists and the Food Nutrition Board of the Institute of Medicine of the National Academies. RS is measured in part by the methodology recommended by the Association of Official Analytical Chemists for measuring dietary fibre. Dietary intakes of RS in westernised countries are likely to be low. However, accurate comparative assessments of dietary intakes between countries, and subsequent epidemiological analysis, are absent due to the lack of consensus over of an agreed, repeatable and simple in vitro method for analysing the RS content of foods. At present, the recognised method is that of McCleary & Monaghan (2002). RS appears to confer considerable benefits to human colonic health, but has a smaller impact on lipid and glucose metabolism. Comparisons between studies are hampered by differences in study design, poor experimental design and differences in the source, type and dose of RS in the ingredients or diets used. It is likely that RS mediates some or all of its effects through the action of short chain fatty acids but interest is increasing regarding its prebiotic potential. There is also increasing interest in using RS to lower the energy value and available carbohydrate content of foods. RS can also be used to enhance the fibre content of foods and is under investigation regarding its potential to accelerate the onset of satiation and to lower the glycaemic response. Due to the difficulties in agreeing on a universal definition and method of analysis for dietary fibre, RS may be included within the term ‘fibre’ on the nutrition labels in some countries but not in others. Pressure to agree a legal definition and universal method of analysis is likely to increase due to the potential of RS to enhance colonic health, and to act as a vehicle to increase the total dietary fibre content of foodstuffs, particularly those which are low in energy and/or in total carbohydrate content.