The relationship between genes and the environment can be compared to a loaded gun and its trigger. A loaded gun by itself causes no harm; it is only when the trigger is pulled that the potential for harm is released. Genetic susceptibility creates an analogous situation, where the loaded gun is one or a combination of susceptibility genes (alleles) and the trigger is an environmental exposure. The key objective of the Environmental Genome Project is to identify alleles that confer susceptibility to the adverse effects of environmental agents. Here we discuss the goals of the Environmental Genome Project, its implications and, in particular, its potential effect on our ability to assess human disease risk in the future.