This thesis examines whether native, heritage, and L2 speakers of Spanish engage a morphological layer of representation in the processing of inflected words, and whether they do so with both regularly- and irregularly-inflected words. Also examined is whether this tendency towards compositional (i.e. morphological rule-based) processing is influenced by kind of language use, in particular productive or receptive response and task implicitness. Experiment 1, a written nonce verb production and acceptability judgment task, indicated that speakers are more likely to use and give higher acceptability ratings to regularly-inflected patterns, though irregular patterns do show some degree of productivity depending on those patterns' type frequency. Experiment 2 was a time-pressured task in which participants were prompted to produce inflected forms of infinitive verbs. Heritage and L2 speakers' accuracy was significantly greater with regular verbs, and their accuracy with irregular verbs was influenced by indicators of lexical knowledge; this indicates that regular verbs may be processed compositionally, whereas irregular verbs are more often stored as wholes. However, native speakers did not show this contrast. Experiment 3 was a primed lexical decision task, indicating that both regular and irregular forms cause morphological priming that is not reducible to formal or semantic priming. The results from all three experiments are largely seen as supportive of a dual mechanism model of morphological processing such as Gor and Cook's (2010) Rules and Probabilities Model in which compositional processing can occur with both regular and irregular forms depending on those forms' type frequency and predictability in the input to which a speaker is exposed. Thus, native, heritage, and L2 speakers are seen as largely similar in this domain of language representation and processing. However, comparison of the three experiments indicates that speakers may be more uniform in tendency towards compositional processing in language comprehension than in language production, particularly in oral production, in which native speakers may possibly engage in more compositional processing. Furthermore, implicit tasks may engage more compositional processing in all speaker groups and native speakers may use more compositional processing overall in oral production responses compared to heritage and L2 speakers. Given the availability of compositional processing to both early and late learners, late learners may benefit from some exposure to explicit morphological rules in the classroom. At the same time, early learners may benefit from more focused exposure to inflectional patterns that are rarer in naturalistic input. [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.]