The Portuguese present perfect (P-PP) is an understudied topic in the field of generative language acquisition. In the past decade, Third Language Acquisition (L3A) has enjoyed special attention in studying how multilingualism works. Researchers have concentrated on the examination of the source of transfer at the initial stages. However, there is a research gap in tense-acquisition studies in Portuguese and the analysis of the developmental stages in L3A. English, Spanish and Portuguese have a temporal-aspectual construction named present perfect (PP) that refers to a past event presented as pragmatically relevant to the present. In this study, I put forward a new proposal of the syntax of the PP, arguing that the past system is composed of two features -[±continuative, ±perfective] -, whose interactions result in four aspects: perfective, imperfective, continuative, and anterior. English and Spanish PP output the anterior aspect by default, but also license continuativity. In turn, Portuguese only allows the continuative aspect with the PP and maps anteriority on the preterit morphology. This study examined the acquisition of functional features of the Present Perfect in L3 Portuguese by bilinguals of English and Spanish; investigating access to the universal grammar (UG) in adulthood and what factors drive L3A. 72 participants completed an online questionnaire testing their knowledge of the syntax, morphology, and semantics of the P-PP. Results indicate that the different distribution of meaning-to-form among these languages poses difficulty for learners, who generally only start to demonstrate representation of the semantics of the obligatoriness of continuative P-PP at the advanced level. Data corroborates that UG-access remains possible in adulthood and that typology plays a significant role both at the initial stages and across the developmental stages, since Spanish, the most closely related language, is chosen as the source of transfer by both English and Spanish natives. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]