For over 100 years, cancer radiation therapy has provided patients with increased survival rates. Despite this success, radiation exposure poses a threat to the progeny of exposed parents. It causes transgenerational genome instability that is linked to transgenerational carcinogenesis. The exact mechanisms in which this instability occurs have yet to be discovered. Current evidence points to their epigenetic nature, specifically changes in DNA methylation. Using mouse and rat models, this thesis investigated the transgenerational effects of radiation in the offspring from parents who received whole body or localized exposure to ionizing radiation (IR). Both types of exposure resulted in significant global DNA hypomethylation in the somatic tissues of the progeny. These changes were paralleled by the significantly decreased levels of methyltransferases and methyl-CpG-binding protein. In summary, our results suggest that both localized and whole body parental exposures to IR result in transgenerational epigenetic instability within the unexposed offspring. / vii, 106 leaves : ill. ; 29 cm.