A wireless power transfer system includes a power transmitter (201) arranged to provide a power transfer to a power receiver (205) via a power transfer signal. The power receiver (205) comprises a first mode controller (709) for transmitting a standby mode exit request to the power transmitter (201) by changing a loading of a communication inductor (209) of the power transmitter (201). The power transmitter (201) comprises a mode controller (405) which controls the power transmitter (201) to operate in a standby mode wherein a presence of the power receiver (205) is detected but no power transfer signal is generated. It furthermore comprises a detector (403) for detecting an impedance change of the communication inductor (209). The mode controller (405) is arranged to initiate a transition from the standby mode to a power transfer mode in response to the detector (403) detecting the impedance change.