The number of people diagnosed with cancer each year will almost double to 21 million cases worldwide by 2030 because of the aging population. Studies of the human genome have demonstrated that as few as 5–10% of adult cancers are due to genetic inheritance. Over 90% of cancers are due to endogenous or exogenous exposure to chemicals and radiation; many of these carcinogenic exposures, to tobacco smoke, for example, are avoidable and thus the consequent disease is preventable. The “exposome” is the concept which captures all carcinogenic exposures across the lifetime, quantified by direct biomarker assessment. Exposomics is in its infancy, but if progress such as has occurred in the Human Genome project occurs in this field, it has the potential greatly to enhance our understanding of the complex interactions and mechanisms of action of environmental exposures. In particular, evidence is increasing that cancer is as much a disease of the epigenome as the genome and that many of these environmental factors act to alter gene expression through changes in the epigenome. Exposomics will enable us better to avoid carcinogenic exposures, to limit the carcinogenic effect of these exposures and to identify potential new targets for developmental therapeutics.