The concept of 21st century skills has become omnipresent in education, training, and personnel selection policies; however, there is little consistency regarding the terms, definitions, or measurement instruments used. A proliferation of terms makes it difficult to identify, operationalize, and teach these non-technical skills, and also goes against the scientific principle of parsimony. This study uses a three-phase approach to quantify the extent of proliferation: A literature survey, a latent semantic analysis, and a hierarchical cluster analysis. Forty 21st century “skills” were identified in the literature search, and analyses revealed a high degree of semantic and psychometric overlap. This suggests that some individual “skills” may not be conceptually distinct, but are rather an array of context-dependent manifestations of a more general underlying competency. To establish greater coherence within the field, we suggest standardizing terms, reducing task impurity with regard to assessment, and revisiting the concept of skills to encompass only higher-order, general competencies.