Whistled languages are communication systems that convey an open-ended set of messages by transposing selected acoustic aspects of the spoken languages that serve as their source. There are two types: those based on non-tone languages, which transpose F2 patterns, and those based on tone languages, which transpose tone melodies. This paper examines basic phonological and phonetic properties of both types of whistled language, with the goal of eliciting their basic similarities and differences. Pitch variation is found to encode segmental distinctions in the first type of language and tonal distinctions in the second. What is common to both is the central role of amplitude modulations, which provide a frame with respect to which segmental boundaries are defined and major segmental classes are distinguished. Examples are taken from whistled languages based on Spanish, Turkish, Moba and Hmong, among others.