Research has shown that humans respond differently to diets and, moreover, that they display varying predispositions to many diet-dependent metabolic and degenerative diseases. The focus of nutritional science is thus shifting from dietary guidelines for populations to individualized foods and diets. It is the aim of nutrigenomics to assign this human diversity in nutritional response to diet – as well as the subsequent consequences to human health – to specific genetic elements. At the same time, evidence suggests that diet itself is a critical determinant of human diversity. This publication focuses on the differences of humans as infants and children with respect to nutritional needs and responses to diet. For this purpose, four main points are discussed, namely 1) How do children differ in view of genetic diversity, environmental inputs, prior imprinting, and resident microflora; 2) What are the immediate and long-term consequences of these differences; 3) Can we accurately assess them; and 4) How can we act on these differences. Supplying answers to some crucial issues, as well as identifying directions for further research and practical applications by the food industry, this publication is an important source of information for all those involved in the subject of diet and individual responses.