Much research has attempted to show direct linear relations between genes and disorder. However, scientists have been discouraged by inconsistent findings based on this simple gene-phenotype approach. The alternative approach is to incorporate information about the environment. A gene-environment interaction approach assumes that environmental pathogens cause disorder, whereas genes influence susceptibility to environmental pathogens. This book brings together contributions from experts from multiple disciplines who discuss: How epidemiological cohort studies can better integrate physiological (mechanistic) measures; How best to characterise subjects’ vulnerability versus resilience by moving beyond single genetic polymorphisms; How gene hunters can benefit from recruiting samples selected for known exposures; How environmental pathogens can be used as tools for gene hunting; How to deal with potential spurious (statistical) interactions, and How genes can help explain fundamental demographic properties of disorders (e.g. sex distribution, age effects).