Purpose: The purpose of this paper is to investigate the potential of already existing skills and competence ontologies to benefit European transparency tools and especially the implementation of the European Qualification Framework. Furthermore, it asks whether any of them could serve as a starting point to develop an International Standard Classification of Skills and Competences to supplement ISCED and ISCO. Design/methodology/approach: This contribution contains a comparative analyses of three systems providing ontologies of skills and competences--DISCO, O*NET and Taxonomy_DB--under terminological and pragmatic aspects. Findings: The analysis identifies O*NET as the most promising candidate to serve European transparency instruments and the EQF. Furthermore, it demonstrates that the development of an International Standard Classification of Skills and Competences, that is suitable for statistical purposes as well as appropriate for practical applications in human resource management and in the area of education, would have to integrate very diverging demands, which so far are being best met by O*NET and DISCO. Research/limitations/implications: The depth of the analysis is not sufficient to serve as an exhaustive guideline to design an International Standard Classification of Skills and Competences. Practical implications: The paper shows the potential of a future International Standard Classification of Skills and Competences for the EQF, for European transparency tools, and for statistical purposes. Originality/value: This article brings a new topic, namely ontologies for skills and competences, into the European debate about competences and their visibility and validation. (Contains 1 figure, 3 tables, and 5 notes.)