Nasality, whether part of a consonant or vowel, has certain phonetic and phonological characteristics that lead to outcomes seen time and again in languages with and without common ancestries. Spanish and Portuguese constitute a particularly fruitful language pairing for studying phonological aspects of synchronic and diachronic variation, given their intimate relationship as well as the array of dialectal variation in each. This research monograph offers a comprehensive exploration of nasals and nasalization in Spanish and Portuguese with a special focus on the role of perception in order to provide insight into how perception informs models of phonetics, phonology and language change. Of interest to researchers and advanced students alike, this volume integrates phonetic and phonological models of speech perception and production, and discusses these with regards to original empirical research on the perception of nasal place features and vowel nasalization by listeners of Peninsular Spanish, Cuban Spanish and Brazilian Portuguese.