This dissertation focuses on a phenomenon that I call vowel intrusion. There are cases where a vowel can be heard between two consonants, yet the phonology behaves as if no vowel is present. These “intrusive vowels” are non-syllabic, and native speakers are often unaware of their existence. 
 I argue that intrusive vowels are a percept resulting from the organization of articulatory gestures. When two consonant gestures have little overlap with one another, there is an acoustic release between them; vowel gestures typically overlap neighboring consonants considerably, and it is possible for an overlapping vowel gesture to be heard in this period of release. 
 Intrusive vowels are not segments. They behave unlike true epenthetic vowels. A typological survey reveals that vowel intrusion happens in consonant clusters that contain a sonorant or a guttural, and that it is always the vowel adjacent to the sonorant or guttural that is heard during the release. Intrusive vowels occur primarily in heterorganic clusters, especially next to geminates; they often disappear at fast speech rates, and in some languages, they occur only within or only between syllables. I argue that these characteristics are best explained in a theory that uses Articulatory Phonology representations (Browman & Goldstein 1986 et seq.).
 	I develop a theory called Timing-Augmented Surface Phonology (TASP), cast within the framework of Optimality Theory. TASP contains constraints on the alignment of neighboring gestures (Gafos 2002) and on the permitted degree of overlap between different gestures. The theory requires a segmental representation as well as a gestural representation. Syllables organize segments rather than gestures, and that inter-segmental gestural alignment is universally non-contrastive. 
 	The same gestural framework describes both the short, schwa-like intrusive vowels often described as “excrescent”, and also a longer type found in Scots Gaelic and Hocank (Winnebago), in which the vowel is heard in two long parts on either side of the sonorant. In the latter cases the sonorant and vowel together behave like a bimoraic nucleus, and are adjoined in a structure similar to vocalic diphthongs. The theory also has implications for the analysis of Hocank accent.