Stable isotope-ratio measurements of the light elements have been used in increasingly important ways to understand processes in geochemistry, hydrology, oceanography, atmospheric sciences, environmental studies, and many other fields. Progress in these fields requires better precision and reproducibility of stable isotope-ratio measurements. Some laboratories are claiming accuracies of 0.02‰; or better for δ13C and δ180. However, δ13C and δ180 analyses of the same sample by different laboratories can differ by more than 0.3‰. Recognizing that isotopic analyses of the same homogeneous material reported from different credible laboratories should yield the same isotopic composition within the uncertainty of the measurements, the International Atomic Energy Agency (IAEA) held an Advisory Group Meeting on stable isotope reference and intercomparison materials for light elements in Vienna from December 11 to 14, 1995.