In recent years new developments have enhanced the interest in measuring isotope ratios with increased sensitivity, reproducibility and accuracy for an increasing number of polynuclidic elements. In geology recent developments include age determinations by samarium-neodymium and lutetium-hafnium methods and the use of selected isotope ratios to construct models for the structure and the evolution of the mantle-crust system. Of primary interest in cosmochronology are the precise measurements of isotope anomalies in solar system materials. In the nuclear field, the interest in obtaining accurate nuclear data to describe the operation of nuclear reactors and to have internationaly well recognized experimental methods leading to accurate inventories of fissile materials throughout the nuclear fuel cycle explains new developments based on mass spectrometry.