We have investigated the SQUID as a voltage-controlled source of microwaves. The low impedance "resistive" SQUID can be a relatively high power ( \sim n W), tunable, and monochromatic source for both on-chip and off-chip applications. Studies of the time-dependent junction phase and the available power spectra as they vary with such device parameters as loaded Q and the SQUID-β= 2πLi c /φ o establish design rules for a well-behaved oscillator. For a VCO βQ \beta Q\geq2 degenerate parametric subharmonic oscillations and chaotic instabilities are observed. Power increase is suggested by the use of voltage-clamped dc SQUIDs and arrays.