This article presents a dual-core quad-mode orthogonal-coupled wide frequency tuning range voltage-controlled oscillator (VCO) using mode control switches to realize the even/odd mode selection. Each core of the VCO adopts a parallel 8-shaped coil structure to avoid the influence of the other orthogonal-coupled one. Together with capacitor banks and varactors, the combination of orthogonal-coupled VCO cores demonstrates an extremely wide frequency tuning range on the basis of the existing range expanding from the dual-mode. The proposed VCO can be classified into two cases with different applications. One is that only one oscillation frequency is required; thus, four modes together show a wide frequency range. The other is that two different oscillation signals can be provided at the same time. The VCO has a measured tuning range of 8.3–21.7 GHz for the combination of low- and high-band cores. It consumes 4–6 mW with a measured phase noise of ?127 dBc/Hz at a 10-MHz offset from a carrier of 9.6 GHz, and the FoM and FoMT are ?179 and ?199 dBc/Hz, respectively. The VCO is designed and implemented in the 65-nm complementary metal-oxide-semiconductor (CMOS) technology with a die area of 0.4 mm2.