According to stringent requirements for insulating thermoset materials, the improvement of thermal, thermo-mechanical as well as electrical performance is a continuous challenge. A potential approach to achieve enhanced heat dissipation, a higher glass transtition temperature (Tg), and sufficient stability against partial discharges and corona discharges is the reinforcement of the thermoset with nano-scaled inorganic fillers. Within this thesis, the development and characterization of thermosetting resins containing inorganic nanoparticles (NP), and nanocomposites for electrical insulation purposes was carried out. The effect of external influences on the property profile of a selected epoxy resin/hardener system (ER) was investigated. It was found, that moisture had a strong influence on the curing reaction and, as a consequence, on the thermo-mechanical properties of the composite. Furthermore, the resin/hardener stoichiometry, the curing temperature and the type of accelerator are influencing the properties of the cured composite. With respect to the composite, silica, alumina and boron nitride NP were selected as they provide superior insulating properties and thermal conductivity. A surface modification of the NP was performed with functional organosilanes, followed by an in-depth characterization of the surface properties. By varying the type, surface functionality and concentration of the selected NP in the epoxy resin, insulation composites with different property profiles were achieved. Regarding the applicability in industrial processes, the viscosity and the shelf-life time of the ER containing NP were investigated. It was found that unwanted interactions of dispersion additives and surface modification reagents with the ER can reduce the shelf-lifetime. By using nanofillers with high thermal conductivity, a significant increase in thermal conductivity was achieved. This effect was enhanced by increasing the filler loading. The thermal conductivity was independent of the surface modification of the nanofillers. The Tg of the composites was affected by the type of surface modification of the NP. Non-covalently bound reagents and additives caused a decrease in Tg, whereas non-functionalized NP lead to an increase in Tg. These investigations were complemented by a dielectrical characterization of the nanocomposites. For composites reinforced with non-functionalized silica and alumina NP, the relative permittivity was reduced to lower values. This is attributed to a higher network density of the composite. Compared to the neat ER, aluminium oxide nanofillers caused lower values for the dissipation factor (tanδ) of the composite. In contrast to this, silica NP lead to an increase in tanδ for the composite. This increase in tanδ is related to a lower volume resistivity of the silica nanocomposite. In contrast to the dissipation factor, the dielectric strength of the thermoset was not affected by the addition of NP. The addition of inorganic NP conferred resistivity against corona discharges onto the insulating composite. Also, the adsorption of moisture by the cured composites was reduced by reinforcement of the ER with inorganic NP. Also, this effect was enhanced by increasing the amount of nanofiller. Based on these results, particularly suited nano-reinforced ER were applied in a vacuum-pressure-impregnation (VPI) process (on lab scale) and in industrial pultrusion processes. By characterization of these nanocomposites, the above described results, concerning thermal conductivity and Tg, were confirmed. Via electron microscopic imaging a homogenous distribution of the nanoparticles in all produced composites was shown. Summing up, in this thesis the applicability of functional NP in resins for VPI and pultrusion processes is demonstrated. The improvement of the property profile of insulating materials by reinforcement with inorganic nanopart