This dissertation explores Spanish copular verbs, "ser" and "estar" (both 'to be' in English), in pre-adjectival contexts within two Spanish varieties: first-language (L1) Chilean speakers from Santiago (N = 29) and second-language (L2) English-speaking learners studying in Chile (N = 31). Bridging sociolinguistics and second language acquisition, it delves into sociolinguistic competence acquisition in an immersive context, focusing on copula development and use. The study collected data through a picture-based oral elicitation task and a written contextualized preference task at three time points for study abroad (SA) participants and a single point for L1 participants. It analyzed both linguistic factors (Adjective Class, Animacy, Experience With the Referent, Frame of Reference, Resultant State, and Susceptibility to Change) and extralinguistic factors (Age, Gender, Grammar Score, Previous Experience Abroad, Parent Origin, Spanish Major/Minor, Study Abroad Site, and social network factors like Number of L1 Contacts, Number of Contact Hours, Reported Closeness With L1 Contacts) to understand how these factors influence copula development and use over time. The findings reveal a progressive alignment of SA learners' copula use with Chilean participants, especially in terms of linguistic factors, albeit surpassing target variety norms in rates of "estar" use in the oral elicitation task. SA learners' development and use were also shaped by extralinguistic factors like Previous Experience Abroad and Reported Closeness to L1 Contacts. Conversely, extralinguistic factors had no significant influence on "estar" selection in the WCPT for Chilean participants. However, Parent Origin significantly affected "estar" use in the PDT, showing Santiago natives whose both parents were also from Santiago favoring "estar" over their counterparts. Further exploration of these factors can provide valuable insights into language acquisition, sociolinguistics, and the intricate interplay between language and context. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]