The processing of structurally ambiguous sentences has proven resourceful in understanding the human parser. In particular, the resolution of globally and temporarily ambiguous relative clauses (RC) preceded by a complex noun phrase (NP) such as "Someone shot [the servant]NP1 of [the actress]NP2 [who was on the balcony]RC" has been found to differ cross-linguistically. In this example, the ambiguous RC can modify either NP1 resulting in high attachment or NP2 which results in low attachment. English monolinguals show a bias toward low attachment, whereas Spanish monolinguals exhibit high attachment preferences (Cuetos & Mitchell,1988). Psycholinguistic studies examining various combinations of L1/L2 present mixed findings on whether highly proficient L2 speakers (e.g. Dussias, 2003; Dussias & Sagarra, 2007) or heritage speakers (Jegerski, et al. 2016, Jegerski 2018) are able to acquire native-like attachment preferences for ambiguous RCs. This study investigates the attachment resolution of temporarily ambiguous RCs in Spanish and English, by heritage speakers and adult L2 learners of Spanish using two behavioral techniques, eye-tracking-while-reading and the self-paced reading paradigm. Additionally, the two NPs were of different biological gender and the disambiguating region either encoded grammatical or stereotypical semantic gender. This design thus allows us to investigate whether different cues to gender can differentially affect online sensitivity to native-like attachment preferences. Eye-tracking results from two groups of heritage speakers and L2 learners reading Spanish sentences revealed that without considering the type of disambiguating cue in the analyses, age of exposure did not lead to any group difference. However, earlier exposure to Spanish lead to greater sensitivity to grammatical gender by heritage speakers. In addition, more proficient bilinguals, regardless of their language background, demonstrated a monolingual-like tendency in Spanish, while bilinguals at lower proficiency levels demonstrated English like attachment resolution for semantic disambiguating factors. The Self-paced reading experiment, however, only demonstrated both groups' sensitivity to semantic, as opposed to grammatical genders. Findings from the present dissertation suggest that attachment preferences by heritage or L2 speakers are not as apparent as the prior literature has assumed, and that large-scale generalizations need to take a more fine-grained approach in investigating the RC attachment preferences of bilinguals. [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.]