This paper is an investigation of nasal vowels from both a synchronic and a diachronic point of view. Data from over 50 languages have been examined (some languages in much more detail than others) in an attempt to distinguish the aspects of vowel nasalization that are "universal" from those phenomena that are language-specific. This study is chiefly concerned with such questions as the following: (1) What is a nasal vowel? (2) Why do nasal vowels arise? (3) What is the historical source of nasal vowels? (4) What is the synchronic origin of nasal vowels? (5) How are nasal vowels used? (6) How do systems of nasal vowels change and disappear? (Author/KM)