Statements like “The human genome is the book of life” were commonly made at the time the human genome sequence was first revealed, reflecting a belief in “genetic determinism”—that a person’s phenotype is determined by his or her genotype. But as we have repeatedly stressed, an organism is not just a product of gene expression. The proteins and small molecules present in any cell at a given point in time reflect not just gene expression but also the influences of the intracellular and extracellular environments. Complementing genomics, the fields of proteomics and metabolomics have emerged to provide a more complete understanding of the relationship between genome and organism.