Heritage grammars, linguistic varieties emerging in the context of intergenerational language loss, are known to diverge from the corresponding full-fledged baseline varieties in principled and systematic ways, as typically illustrated by errors made by heritage speakers in production. This dissertation examines "covert" restructuring of aspect in heritage Russian, a grammatical reorganization of the perfective-imperfective opposition not manifested in overt errors. The aspectual system instantiated in acrolectal varieties of heritage Russian is shown to exhibit signs of covert divergence from the baseline system at the interface between syntax and discourse-pragmatics, manifested in a reduction of pragmatically-conditioned functions of the imperfective aspect with total single events. This emerging restriction leads to a gradual shift from a privative aspectual opposition in baseline Russian, where imperfective is the unmarked member, to an opposition of the equipollent type. Experimental evidence presented suggests that heritage speakers differ from baseline Russian speakers in their use, acceptability ratings, and accuracy of interpretation of the imperfective aspect. In Russian, both aspects are compatible with completed events; however, aspectual competition is resolved in favor of the imperfective in the presence of discourse-pragmatic triggers that condition the general-factual functions of the imperfective: statement of fact, annulled result, thematicity and backgrounding. Assuming a multi-level approach to aspect, I maintain that the two aspectual systems converge on the level of the verbal predicate, where aspectual values of activities and accomplishments reflect compositional telicity, but diverge on the level of sentential aspect, where the contribution of telicity may be overridden by grammatical aspectual operators and discourse-pragmatic aspectual triggers. The restructuring of aspect in advanced heritage grammars affects the highest level of sentential structure, a domain in which syntactic information is mapped onto discourse-pragmatic information (the C-domain). In addressing the role of linguistic input in heritage language acquisition, the dissertation examines additional data from bilingual Russian-English speakers, including parents of heritage speakers. While bilingual speakers pattern with monolingual controls on comprehension tests, they differ from monolinguals in production of the imperfective with total single events, suggesting that competence divergence in advanced heritage grammars may be linked, across generations, to impoverished performance on C-domain properties. [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/en-US/products/dissertations/individuals.shtml.]