There has been an evolution in our understanding of the causes of undernutrition and of the nutrition intervention programs that should be prioritized. This article discusses why nutrition programs have shifted their primary emphasis from control of protein deficiency, to energy deficiency, and now to micronutrient deficiencies. It has become recognized by the nutrition community that micronutrient malnutrition is very widespread, and is probably the main nutritional problem in the world. The most commonly used strategies for micronutrient deficiency control are supplementation and fortification, because they are cost-effective and to some extent, relatively easy to deliver. They have important limitations, however. Relatively little emphasis has been placed on food-based approaches to control micronutrient malnutrition. Evidence from several past studies, including the Nutrition Collaborative Research Support Program (N-CRSP), indicated a strong positive association between animal source food (ASF) intake, micronutrient status, and many human functions. This association motivated the intervention studies supported by the Global Livestock CRSP and described in this supplement, which found benefits of increasing ASF intake. In contrast to the common assumption that increasing consumption of ASF in poor communities is infeasible, and will only cause environmental problems, the articles in this supplement show the potential economic benefits of animal ownership in poor communities, and provide examples of innovative programs that have increased local production and consumption. Much more communication is needed among the nutrition, agriculture and development communities to achieve improved dietary quality for poor populations.