Tonogenesis is the development of distinctive tone from earlier non-tonal contrasts. A well-understood case is that of Vietnamese (similar in its essentials to that of Chinese and many languages of the Tai-Kadai and Hmong-Mien language families), where the loss of final laryngeal consonants led to the creation of three tones, and the tones later multiplied as voicing oppositions on initial consonants waned. This is by no means the only attested diachronic scenario, however. There is tonogenetic potential in various series of phonemes: glottalized vs. plain consonants, unvoiced vs. voiced, aspirated vs. unaspirated, geminates vs. simple (and, more generally, tense vs. lax), and even among vowels, whose intrinsic fundamental frequency can transphonologize to tone. But the way in which these common phonetic precursors to tone play out in a given language depends on phonological factors, as well as on other dimensions of a language’s structure and on patterns of language contact, resulting in a great diversity of evolutionary paths in tone systems. In some language families (such as Niger-Congo and Khoe), recent tonal developments are increasingly well-understood, but working out the origin of the earliest tonal contrasts (which are likely to date back thousands of years earlier than tonogenesis among Sino-Tibetan languages, for instance) remains a mid- to long-term research goal for comparative-historical research.