A short review of the field of internal conversions. Isomeric transitions teach us many details of nuclear structure. In these studies electromagnetic theory is considered as a "tool". It is a quite quantitative tool in the case of "internal conversion" - a phenomenon which has been widely studied for many years. Internal conversion takes place in competition with γ-ray emission: a fraction of the nuclei in excited states decay by γ-ray emission, the remaining fraction by transferring the energy to K, or L, etc. electrons in the atomic shell. Thus the lifetime of an excited nuclear state depends on the internal conversion coefficient. As internal conversion must be expected to depend on the details of the electronic environment, the lifetime of an isomeric state depends on the state of chemical combination of the isomer - as was recently shown explicitly in one case, that of Te-99m(6hr.).