Owing to their unique potential applications, including electron guns, microwave power amplifiers, electron microscopy and flat panel displays, an intense research effort has been devoted to the design and fabrication of cold cathode electron emitters exhibiting low operation voltage, high current emissivity, and increased durability under poor vacuum conditions. Research in this field indicated that multiscale field electron emitters are superior compared with single-length scale ones. This chapter overviews the current state of the art of the hierarchical field emitter technologies, demonstrating their great potential for future electron device applications.