An adaptive system for efficient and long-range wireless power delivery using magnetically coupled resonators responds to changes in a dynamic environment, and maintains high efficiency over a narrow or fixed frequency range. The system uses adaptive impedance matching to maintain high efficiency. The wireless power transfer system includes a drive inductor coupled to a high-Q transmitter coil, and a load inductor coupled to a high-Q receiver coil. The transmitter coil and receiver coil for a magnetically coupled resonator. A first matching network is (i) operably coupled to the drive inductor and configured to selectively adjust the impedance between the drive inductor and the transmitter coil, or (ii) is operably coupled to the load inductor and configured to selectively adjust the impedance between the load inductor and the receiver coil.