Glass and glass ceramics are promising new materials for high temperature capacitors. A survey of present dielectric materials and capacitors shows that major improvements in energy density, volumetric efficiency and performance is achieved by increasing capacitor reliability at high temperature. Glass and glass-ceramics are candidate materials for high temperature capacitors because of their low dielectric loss and high breakdown strengths. Synthesis of glass ceramics begins by quenching glass sheet (300 micron thick) followed by recrystallization into high permittivity ferroelectric compounds. The high temperature dielectric properties of a fresnoite glass ceramic system were explored and the dielectric loss value was below 2% for temperatures less than 350°C. In addition, commercial thin glass sheets (thickness = 50 microns) with high silica content were characterized at high temperature and were found to have very low dielectric loss up to 200°C. Both glass and glass ceramic dielectrics were fully characterized by highly accelerated life testing and the show excellent performance in terms of projected capacitor life at temperatures up to 300°C.