IN THE LONG HISTORYof scientific investigation of musical instruments the flute has been given particular attention, primarily because of its apparent simplicity. Yet many of the physical factors that determine its behavior have not been well documented. In my experiments I have tried to look at some of these factors quantitatively, concentrating on a comparison of the passive resonance and blown frequencies of the flute, on the details of the blowing mechanism at the mouth hole, and on the energy conversion and losses of the instrument when it is regarded as an oscillator with a resonant circuit and nonlinear feedback. It turns out that the momentum and arrival time of waves on the blowing jet determine the loudness and pitch of the sounded note. Details of the flutist's empirically learned technique can be explained in these terms.