The application of molecular biology techniques and the success of the Human Genome Project have opened a new era for both Medicine and Nutrition. To date, at least 1,000 human genes causing disease have been identified and partially characterized, 97% of which we now know that are the cause of monogenic diseases. However, other diseases such as obesity, cardiovascular disease, diabetes, and cancer are due to complex interactions between several genes and environmental factors. In spite of the many association studies, over 600 published since 2002, the molecular base of chronic diseases is still uncertain. Information about nucleotide polymorphisms and haplotypes maps is an additional resource for identifying genes implicated in diseases. Genomic development gets close, however we frequently do not accurately know the dietary components and their mechanisms that importantly influence on genetic information expression and its pathologic impairments. The food industry has the opportunity for utilizing the bioactive components of foods to improve health and prevent diseases while considering the consumers' genetic constitution. This new era of molecular nutrition--gene-nutrient interactions--may evolve in several ways, although two of them are essential. On the one hand, the study of the influence of nutrients on gene expression (nutrigenomics) and, on the other hand, to know the influence of genetic variations in the organism response to nutrients (nutrigenetics).