Language is one of the essential tools used to segment the continuous stream of experience into events. In this process, the choice of words and grammar frames events in different ways. Grammatical aspect plays an important role in representing an event as a complete whole (perfective: peeled) or as a dynamic process (imperfective: was peeling). Aspect systems differ crosslinguistically in terms of aspect grammaticalization, the correspondence between temporal meanings and aspectual forms, as well as grounding of aspectual forms in perceptual characteristics of events. This dissertation research investigates the relationship between aspect and mental representations of events in two aspectual languages, English and Russian, across three domains of language and cognition: (1) event conceptualization; (2) processing of aspect temporality; and (3) event memory. The findings reveal that language-specific aspectual systems have a profound impact on event cognition. Specifically, fully grammaticalized aspect with strict correspondence between aspect forms and distinct temporal distributions in Russian resulted in stronger sensitivity to event stage in event conceptualization, elicited grammatically-oriented processing of aspect temporality, and increased the salience of event stage for memory. In English, where aspect is partially grammaticalized and the correspondence between temporal meanings and aspectual forms overlaps, subjective perspective on an event played more important role than event stage for event conceptualization, aspect was processed as a source of information for event model update, and event memory was impacted by aspect at the level of event construal, rather than event stage. In sum, stricter aspect enhances the salience of perceptually available event stage in mental representations of events; flexible aspect contributes to the information provided by perceptually available event stage to form an event's mental representation. [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.]