Chromosomal instability is characterized by an increased rate of chromatid and chromosome rearrangements occurring multiple generations after exposure to ionizing radiation. Although chromosomal instability has been observed in many different cell types after exposure to ionizing radiation, the mechanisms perpetuating the manifestation of this instability phenotype are unknown. This review explores the current evidence concerning the role of dicentric-mediated bridge-breakage-refusion cycles and the role of recombination at interstitial telomere bands in mediating chromosomal instability. In addition, the contribution of genetic and epigenetic factors are discussed with regard to the predisposition of cells to chromosomal instability.