This book introduces fully-integrated voltage-controlled oscillators (VCOs), which use the right-handed LC resonator, the left-handed LC resonator or the composite right/left-handed (CRLH) LC network. The CRLH oscillators display the property of multi-resonance resonator, and they can provide multi-band frequency signals or output concurrent signals. Frequency tuning hysteresis is found for the varactor-tuned multi-resonance oscillators. Mode switching CRLH dual-band oscillators are included and the operation principle of CRLH oscillators are addressed. The CRLH LC network is made of capacitor, varactor, inductor and transformer.