Dr. Kristi Winters (GESIS) and Janek Bruker (formerly of GESIS) discuss the use of international standard classifications when harmonizing social science data. This is video 3 in a series of 4 videos designed to provide introductory information on variable harmonization. Topics include an introduction to social science variable harmonization, examples from international social science surveys, the use of international standard classifications and how to use metadata to construct FAIR variable harmonization documentation. Topics in this four-part educational video series include: an introduction to social science variable harmonization, ex ante and ex post harmonization strategies, examples from international social science surveys (including the European Values Survey), the use of international standard classifications, and how to use metadata to construct FAIR variable harmonization documentation. This video was created for the Consortium of European Social Science Archives (CESSDA). For more information visit www.cessda.eu The course material comprises the presentation "Variable Harmonization in the Social Sciences" (http://doi.org/10.5281/zenodo.3924955) and the full series of 4 videos: 1. An Overview of Concepts and Strategies http://doi.org/10.5281/zenodo.3924208 (This video is also available for viewing on Youtube) 2. Process, Challenges and Quality Criteria http://doi.org/10.5281/zenodo.3924218 (This video is also available for viewing on Youtube) 3. International Standard Classification http://doi.org/10.5281/zenodo.3924227 (This video is also available for viewing on Youtube) 4. Documentation and Best Management Practices http://doi.org/10.5281/zenodo.3924241 (This video is also available for viewing on Youtube)