Analog RF front-end circuits are typically designed to perform one specific task, while key parameters such as dynamic range, bandwidth and selectivity are fixed by the hardware design and not by the communication system in an adaptive way. As a result, today's receiver topologies are designed to function under the most stringent conditions, which increases circuit complexity and power consumption. However, the conditions under which the RF circuits operate are not fixed but vary widely and depend upon a multitude of factors. Therefore, a concept of design for adaptivity is introduced in this paper. It establishes a trajectory for an all-round performance characterization of adaptive oscillators with an explicit qualitative and quantitative description of all the existing relations and tradeoffs among the oscillator performance parameters. As a proof of concept, an 800-MHz adaptive voltage-controlled oscillator is designed with phase-noise tuning range of 7 dB and more than a factor 3 saving in power consumption, suitable for unobtrusive mobile equipment, foreseen to operate in this band.