This paper reviews the typology and distribution of vowel systems which include nasalized vowels. It is well-known that languages with distinctively nasalized vowels have an equal or lower number of nasalized vowel qualities than of oral vowel qualities. However, there are interesting areal differences in the distribution of systems with equal and fewer numbers of nasalized vowels. Languages in Africa usually have fewer nasalized than oral vowels; languages in the southern part of the Americas more often have equal numbers of oral and nasalized vowel qualities. The latter pattern is sometimes associated with a morphological function for vowel nasalization.