You know how to whistle don't you? Just put your lips together...and blow.
Lauren Bacall, To Have and Have Not (1944)

If only it were that simple! Everyone knows what whistling is, but very few know quite how it works, other than you put your lips together and make a funny noise. However what actually happens is that while you whistle your lips vibrate subtly and so does the air around your lips and inside your mouth, this in turn causes the air molecules in front of you to vibrate and create compressions and depressions in the air. These compressions and depressions are what causes a sound wave, and the closer together these compressions and depressions the higher the note will be. You lower the pitch by increasing the size of cavity in your mouth (moving your tongue back and your jaw down) and raise the pitch by decreasing the size of cavity in your mouth (moving your tongue forwards towards your teeth and your teeth closer together). If you are an expert you can alter the sound with your tongue as well and make warbling sounds.

There are four main steps to whistling normally, like a builder or plumber. First, you must moisten your lips to make a smoother edge for the air to flow through. Then put the point of your tongue against your bottom teeth and arch your tongue while also relaxing it. Now make an 'o' shape with your moistened lips, and blow gently. When you make a whistling sound you can develop it to alter its pitch and finally start whistling a tune.

The top two whistling tunes: Indiana Jones and The Great Escape.

There are other more complex ways to whistle and these work in a different way to the other whistles mentioned before. These methods are done using your fingers usually, and produce the air compressions and depressions by splitting the air over a surface, thus one side of the surface the air is vibrating more than the other side. These methods are less flexible than the other method and it is harder to vary the pitch.

Whistling sometimes has a strange effect on people they either hate it and try to stop you whistling or tolerate it and pretend they like it, usually to annoy the people who hate it. However the people who hate you whistling most are the ones that can't whistle at all. There are theories about whistling being genetic and this does seem to be true. This is probably mainly to do with the lip muscles, skin on the lips.

Some people do like whistling though and for these people there are whistling concerts featuring the music of famous whistlers (such as Fred Lowery, Ronnie Ronalde, Roger Whittaker, Elmo Tanner, Muzzy Marcellino, Bing Crosby, Purves Pullen, Al Jolson, Toots Thielemans, Ron McCroby, and Joel Brandon to name a few). For some reason nearly all whistling concerts are held in America, perhaps the Americans make the best whistling sound.