This paper is concerned with the ways of how foreign words are adapted into a host language, Korean. Specifically, this paper examines several kinds of adapted forms with an inserted vowel and argues that -insertion occurs not only to accommodate the release feature of a foreign segment but also to enforce the phonological requirements of Korean into the adapted forms. Furthermore, this paper argues that these two types of -insertion occur in different stages of adaptation, unlike the suggestion made by Silverman (1992). In Section 2, this paper reviews the arguments in H. Kang (2002), which argues that -insertion for‘bus’ occurs in Perceptual Level whereas -insertion for [auth ain] ‘outline’ occurs in Operative Level. This paper provides detailed arguments of why the distinction is necessary. In Section 3, this paper considers how English stops are adapted into Korean. It shows that word-final stops are adapted into 2 ways. Following Y. Kang (2002), this paper argues that stop-final English words are sometimes adapted as vowel-final since the word-final stops are optionally released. This paper also considers words with an internal voiced coda stop. Interestingly, these voiced stops are sometimes adapted as CV, not as C, even if they are unreleased This paper argues that vowel-insertion occurs in this case to faithfully maintain Contrast of voiced/voiceless consonants of the source language in the host language. It also provides some arguments why it is a voiced segment, not a voiceless segment that triggers -vowel insertion.