A review is given of geologic investigations using stable isotopes and changes in their abundance. Many natural processes tend to concentrate particular isotopes by a factor of several percent. Four creationist applications arising from this natural isotopic enrichment are considered. First discussed are large scale errors in C14radiometric dating of fresh water Mollusk shells due to C12 isotope exchange. It is shown that this age-determination uncertainty may also affect all other radiometric dating methods. Popular concepts of evaporite deposition and continental drift, that are dependent upon long geologic ages, are discussed. Recent stable isotope data which can be used to contradict these ideas is interpreted. The final application concerns information from extraterrestrial isotopes. Looking ahead, future research with stable isotopes will concentrate on paleotemperatures which may provide additional evidence for a preflood vapor canopy.