The International Research on Infant Supplementation trials emerged as an attempt to develop a credible evidence base to guide policy decision making in this area. The fact that infant diets in developing country settings are more often deficient in multiple micronutrients rather than in single nutrients and/or energy was increasingly recognized during the 1990s. The concept of a "foodlet," a crushable hybrid between a tablet and a food that is water dispersible, was developed at the first IRIS meeting in Rio de Janeiro in 1999. Trials were performed in 4 countries: Indonesia, Peru, South Africa, and Vietnam. Four different formulations of foodlets were tested: a daily placebo supplement, a daily iron supplement, a daily multiple micronutrient supplement, and a weekly multiple micronutrient supplement with a placebo on the other 6 d. The multiple micronutrient foodlets contained adequate daily intakes of 13 micronutrients considered most likely to be inadequate in infant diets. The foodlets were produced in Peru and distributed to all 4 of the country study sites. The methods used in the efficacy trials were standardized across countries, and the trials were carried out in infants 6-11 mo of age for 6 mo. Anthropometry was measured monthly and morbidity checked daily. Blood samples were collected at baseline and at the end of the trial. The data and the biological samples collected in each country were analyzed centrally. The results of this remarkable international collaboration are encouraging and, hopefully, will spur the development of programs in this area of nutrition interventions.