In most second language studies, learners’ native variety is assumed to be homogenous, regardless of their regional variety. Nevertheless, regional varieties differ in non-trivial ways and such differences need to be considered when analyzing second language acquisition. This book examines the role of the native dialect in non-native perception and production in the specific case of Cuban and Peninsular Spanish as native varieties and of English vowels as in the words /hat/, /hut/, and /hot/ as the target. This study takes shape around the main research question of whether potentially systematic differences between vowels in the native dialects of Cuban and Peninsular Spanish would produce matching phonetic differences in non-native perception and production of English vowels. This question was addressed in three experiments that compared native vowels in these Spanish varieties, as well as the perception and production of the target English vowels as in /hat/, /hut/, and /hot/ by Cuban and Peninsular Spanish learners. I concluded that the native dialect was one of several factors generating differences between the two groups of L2 learners.