The Linguistic Association of Korea Journal, 21(2), 21-42, Korean vowel shortening, operating at the level of the foot, is a typical case of trochaic shortening motivated by the complete prasing of syllables into feet, As an anti-trapping effect, trochaic shortening saves a prosodically trapped light syllable in an uneven trochaic context like [H L]. The mechanism of extrasyllabification is closely related to and thus, plays a crucial role in Korean vowel shortening. Extrasyllabification of the final consontant is generally preferred over vowel shortening. When it would yield an unsyllabified consonant, extrasyllabification is replaced by vowel shortening. The major theoretical finding of this study is the active operation of throchaic shortening in an iambic system, Korean. This provides a new perspective in the typology of vowel shortening. Shortening processes, either trochaic or iambic, have been generally described as a typical characteristic of trochaic languages, mainly stemming from the so-called lambic/Trochaic Law. Only lengthening processes such as iambic lengthening have been proposed as signigicant means of quantitave adjustment in iambic languages. As a foot-based process, however. trochaic shortening is metrically well-motivated in the iambic system of Korean.