The “nontargeted effects” of ionizing radiation, including bystander effects and genomic instability, predominate after low dose exposures and dominate response outcomes. These effects are unique in that no classic mutagenic event occurs in the cell showing the effect. In the case of bystander effects, cells which were not in the field affected by the radiation show high levels of mutations, chromosome aberrations, ROS, and membrane signaling changes (i.e., horizontal transmission of mutations and information which may be damaging). This can be contrasted with the case of genomic instability, where generations of cells derived from an irradiated progenitor appear normal, but then lethal and nonlethal mutations appear in distant progeny (i.e., vertical transmission). These phenomena are characterized by high yields of mutations and distant occurrences of events both in space and time. This precludes a mutator phenotype or other conventional explanation and appears to indicate a generalized form of ROS-mediated, stress-induced mutagenesis, which is well documented in bacteria. The nature of the signal traveling between irradiated and unirradiated cells and organisms is currently unknown, but recent evidence suggests that there may be a physical component such as a vibration wave involved. UV photon-mediated transmission has also been documented and the latter mechanisms can induce the release of exosomes, which by themselves can induce bystander effects when added to recipient cells. This review will discuss the phenomenology of nontargeted effects both in vitro and in vivo; it includes recent data suggesting that excitation decay-induced photons in the UVA range lead to exosome release, resulting in mitochondrial malfunction and elevated ROS in recipient cells. Photons, calcium, and neurochemicals are important factors in signal production, while the exosome cargo and cytokine mediated pathways, especially TGFb, are implicated in response to the signal. Important clues from the field of chemical ecology are reviewed to highlight the fact that signaling is very widespread in biota, and that many mechanisms and signals are extensively researched in the field. By highlighting some key challenges and controversies concerning the mechanisms and, more importantly, the reason these effects exist, we will discuss current ideas about the wider implications of nontargeted effects in evolution and environmental biology.