[eng] This paper reports two experiments on nonnative vowel perception and production. In Experiment 1, three groups of Catalan learners varying in English proficiency were tested on their ability to discriminate seven Catalan-English (C-E) and four English-English (E-E) vowel contrasts. The vowel contrasts were natural speech tokens obtained from native Catalan and native American English speakers. On average, listeners distinguished the C-E /i-ɪ/ contrast relatively well, and they could partially distinguish /i-i/, /u-u/, and /a-ɑ/, but they had great difficulty with the /a-ʌ/, /a-æ/ and /ɛ-ɛ/ contrasts. As for the E-E pairs, the learners could discriminate the speech sounds in the /i-ɪ/ and /u-ʊ/ pairs, suggesting that learners may have established new phonetic categories for /ɪ/ and /ʊ/. In Experiment 2, a subgroup of the Catalan learners and a control group of native English speakers produced words containing one of the English vowels /i/, /ɪ/, /ɛ/, /æ/, /ɑ/, /ʌ/, /ʊ/, and /u/. Vowel accuracy was assessed by means of acoustic measurements and by native listener judgments. The acoustic measurements revealed that, in spectral terms, learners produced vowels that were less peripheral than the native English (NE) versions, although there was a tendency for vowel expansion as a function of language proficiency. Vowel duration in the tense-lax vowel pairs also progressed toward more nativelike values in the productions of the more proficient learners. Finally, the NE listener judgments showed that most learners produced the vowels /ɪ/, /æ/, /ʊ/, and /u/ intelligibly but with significantly lower goodness ratings than did the NE speakers.