Recent measurements of carbon isotopes in carbon dioxide using near-infrared, diode-laser-based cavity ring-down spectroscopy (CRDS) are presented. The CRDS system achieved good precision, often better than 0.2‰, for 4% CO₂ concentrations, and also achieved 0.15–0.25‰ precision in a 78 min measurement time with cryotrap-based pre-concentration of ambient CO₂ concentrations (360 ppmv). These results were obtained with a CRDS system possessing a data rate of 40 ring-downs per second and a loss measurement of 4.0?×?10 -11  cm -1  Hz -1/2 . Subsequently, the measurement time has been reduced to under 10 min. This standard of performance would enable a variety of high concentration (3–10%) isotopic measurements, such as medical human breath analysis or animal breath experiments. The extension of this ring-down to the 2 µm region would enable isotopic analysis at ambient concentrations, which, combined with the small size, robust design, and potential for frequent measurements at a remote site, make CRDS technology attractive for remote atmospheric measurement applications.