Most of the important biological effects associated with the exposure to ionizing radiations are mirrored at the chromosomal level. In all cases, changes in the levels of cytogenetic effects are associated with changes in absorbed dose, dose rate and radiation quality. Some of the complexities associated with the quantitative description of such changes in response can be circumvented by appealing to concepts embodied in what has been called the “mean inactivation dose”. Additional metrics designed to provide LET-dependent “signatures” of damage have been employed with moderate degrees of success. These, along with some alternative approaches, are discussed in an effort to stimulate discussion, and to further work leading to a better understanding of mechanisms involved in the production and significance of chromosome aberrations after exposure to ionizing radiations.