Comparing with other dielectric waveguides, NRD (nonradiative dielectric guides) presents advantages of ease of fabrication, low transmission loss, and absence of radiation from bends and discontinuities, making it suitable for realizing compact and high-performance millimeter wave integrated circuits. First, we study the EM theory of NRD to observe the characteristic affected by NRD geometric parameters and introduce multi-mode parameters to analyze mode coupling phenomena in bend and two-layer NRD structures. In order to promote NRD circuit application and transmission performance, we also study an integrated transition between microstrip line and NRD and mode suppressing technique. Finally, the structures mentioned above are all integrated in circuit application.