The paper discusses the options for a conceptual framework to describe how the knowledge created and acquired in VET is changing due to technological innovation and the shift towards a knowledge economy. The discussion sets out from the question how vocational or professional knowledge may be distinguished from other forms of knowledge and what philosophical and epistemological traits may underpin this distinction. Building on an analysis of 'intrinsic' and 'extrinsic' conceptions of knowledge, the paper explores how appropriate descriptors for the classification of theoretical or propositional knowledge as well as practical knowledge may be identified. As a result, a proposal for structuring vocational knowledge is presented. The concluding part addresses the question how the proposed categories may serve to characterise changes in vocational knowledge and explores the requirements for applying the conceptual framework in empirical studies on the effects of technological innovation and societal developments.