© 2018, Springer-Verlag GmbH Deutschland, ein Teil von Springer Nature. Stable isotopes are increasingly used to trace microbial activities and metabolic pathways and are widely applied in microbiology, biochemistry, and risk assessment. This development is tightly linked to advance of mass spectrometric instrumentation as the key analysis for stable isotopes. Also the concepts for stable isotope tracing are progressing fast. We briefly review such concepts and indicate some of our own studies.