The goal of the Ph.D. thesis is the study and analysis of the intersectoral knowledge diffusion, that stems from Research and Development (R&D). This knowledge concerns not only patent protection and trademark rights but also knowledge and ideas transferred to sectors via the R&D activities performed by others. The use of technological coefficients and input-output multipliers, combined with the available sectoral R&D expenditure and patent data, allows for the calculation of R&D multipliers. The predictive ability, both short and long-term, of these multipliers, as well as their efficiency, is studied. In addition, econometric models are constructed, that study the contributing factors to intersectoral knowledge diffusion. The form and construction of the aforementioned econometric models is based on the adaptation and modification of models that study the diffusion of knowledge at the interregional or state level. Moreover, particular attention is given to the case of Nanotechnology. Developments, trends and patent production originating from the Research and Development activities of Nanotechnology are measured and correlated with the rest of the research activity.