To date, there are still only a handful of dwarf star isotopic abundances in the literature and even fewer of those are from exoplanet host stars. Past isotopic searches have been hindered by limited sensitivity and resolution, strong telluric absorption, and the opacity due to millions of other molecular absorption lines that dominate the observed spectrum of cool stars. Now, isotopic abundance analysis is possible via high resolution spectroscopy and is the next logical step for many cool exoplanet host stars. Because the interpretation of planetary isotope ratio measurements directly depends on complementary host star measurements, it is of the upmost importance to build the stellar isotopic abundance database-- especially as novel isotope detections in exoplanet atmospheres are being reported. Here, I provide an overview of stellar CNO isotope ratios (12C/13C, 14N/15N, and 16O/18O), how certain fractionation mechanisms provide clues to an exoplanet’s formation location relative to “snowlines” and discuss what planetary isotope ratios can tell us about exoplanet atmospheric composition and evolution. I will also discuss the detectability of stellar and planetary CNO isotope ratios from ground-based and/or space-based observatories--in particular, in which planetary systems we may measure both host star and exoplanet CNO isotope ratios.