In this paper, we report our recent research works on the W-band waveguide-to-CPW transitions for various MIMIC applications. For this, the transitions operating in a frequency range of 85 ~ 100 GHz are designed, fabricated and characterized. The designed waveguide-to-CPW transition is optimized to achieve low loss by using an EM field solver of HFSS. From the measurement, an insertion of -2.2 dB and a return loss of -23.86 dB, respectively, were obtained at 94 GHz. The average insertion loss of waveguide-to-CPW back-to-back transition is -2.5 dB in a frequency range of 85 ~ 100 GHz.