Genome stability of every species depends on complex interaction of predefined and environmentally induced genetic and epigenetic states. Predefined states consist of chromatin structure and cell metabolic processes such as DNA repair, radical scavenging and cell signalling, whereas induced states depend on interactions with the environment. Organisms are able to respond to a changing environment by various alterations in their somatic cells as well as in their germline and progeny. In this book, we will describe various phenomena associated with the maintenance of genome stability. These include genetic and epigenetic responses to various stresses in exposed cells and organisms, bystander and, bystander-like effects, transgenerational changes in genome stability and stress tolerance in bacteria, plants and animals.