Driven by the urgent requirement for miniaturization, multi-functionalization, and high performance of electronic devices, embedded technology in electronic packaging is developing rapidly. The design and fabrication of polymer composite materials with high capacitance density and good compatibility with current Printed Circuit Board (PCB) technology are of primary importance for the development of embedded capacitors. The commercialized embedded capacitor materials can only offer low capacitance density; so, the commercial embedded capacitors only replace a small part of the surface-mounted capacitors. The development of advanced embedded capacitor materials is a long-standing work, and major obstacles involve the balance of the dielectric and mechanical properties, as well as reliable varnish fabrication, film coating, and lamination with copper foil, etc. In this chapter, we try to summarize some important aspects of designing and fabricating polymer-based embedded capacitor materials.