This paper presents passive integrated circuits for millimeter-wave transmitters and receivers implemented in a 45-nm CMOS silicon-on-insulator (SOI) process. The advantages of SOI over bulk CMOS are discussed for millimeter-wave passive circuits. First, a single pole double throw (SPDT) switch demonstrates a measured insertion loss of less than 1.7 dB at 45 GHz and third-order intermodulation intercept point (IIP3) of 18.2 dBm. Second, a double-balanced passive in-phase/quadrature (I/Q) mixer exhibits a conversion loss of 8.35 dB at 44 GHz and IIP3 of 15.5 dBm. At a fixed IF of 200 MHz, the minimum I/Q gain and phase imbalance is 0.25 dB and 1.9°. The passive mixer and SPDT switch results demonstrate a record minimum insertion loss and linearity performance for the passive millimeter-wave circuits.