term), being in fact rather extraordinary realizations of the languages spoken in the re­ gions where they occur. They utilize the vocabulary, grammar and, in many cases to a large extent, the phonology of the local speech. However their phonetic system is profoundly modified acoustically and (in some cases less so) from the point of view of articulation, because the glottal tone of every­ day communication, the "voice", is repl aced by a whistl e which carries the in­ formation. The advantage of this procedure, from the point of view of the user, is a vastly increased range as well as, under certain circumstances, a degree of secrecy. It will be shown that whistled languages appear in two main, very different forms.