This paper presents a millimeter waveguide-to-microstrip line transition based on E-mode coupling. It uses a standard W-band waveguide and a microstrip line made on alumina substrate. It has been designed for the center frequency of 94 GHz. A back-to-back transition has been done and measured between 90 and 100 GHz. A bandwidth of more than 12% with insertion loss of −5 dB is demonstrated for a microstrip length of about 21 mm. Complementary measurements show that the transition itself achieves 0.6-dB losses.