Voluntary feed intake of pigs determines nutrient intake levels and thus has a great impact on efficiency of pork production. Adequate feed intake is hard to maintain on many farms and is then an important factor limiting productivity. Stressors (for example, hot temperature, increased stocking density and reduced health status) together with genotype influence feed intake and thus growth. Furthermore, dietary factors, including energy density, deficiencies or excesses of nutrients, antibiotics, flavours, feed processing, and availability of water influence feed intake. Differences in intake of pigs fed different batches of ingredients have rarely been described. The spectrum of factors that affect voluntary feed intake is very broad. The purpose of this paper is to highlight some of these factors, to describe issues relating feed intake to feed evaluation, and to give an overview of feed evaluation research at Prairie Swine Centre. Various stressors influence voluntary feed intake in swine. Stressors can be grouped into environmental (temperature, humidity, air circulation, etc), social (space allocation, group size, re-grouping, etc.), and immunological (disease, pathogen concentration, etc.) factors. The DE content of feed appears to be an important factor to determine feed intake of grower-finisher pig, and determination of DE content of individual ingredient samples is thus important. Ingredient factors other than DE content may play a role as well. Because feed intake is the ultimate driver of pig performance, and thus the barn throughout, this is a critical area of future research.