Radiation induced bystander effects are effects observed in unirradiated cells which receive signals from irradiated cells. Bystander effects include DNA damage, chromosomal aberrations, changes in gene expression, oncogenic transformation and cell death. Bystander signals can be transferred to surrounding cells either by gap junctional intercellular communication or by the production of soluble extracellular factors released from irradiated cells. Recently, exosomes have been shown to play a role in transferring signals from irradiated to non-irradiated cells. This review summarises a recent body of work on radiation induced bystander signalling, focusing on calcium, reactive oxygen and nitrogen species and on membrane signalling.