Time is central to human cognition, both in terms of how we understand the world and the events that unfold around us as well as how we communicate about those events. As such, language has morphological systems, such as temporal adverbs, tense, and aspect to convey the passage of time. The current study explored the role of one such temporal marker, grammatical aspect, and its impact on how we understand the temporal boundaries between events conveyed in narratives. In Experiments 1 and 2, participants read stories that contained a target event that was either conveyed with a perfective (e.g., watched a movie) or imperfective aspect (e.g., was watching a movie) and engaged in an event segmentation task. Events described in the perfective aspect were more often perceived as event boundaries than events in the imperfective aspect, however, event duration (long vs. short) did not impact this relationship in Experiment 2. Experiment 3 demonstrated that readers were sensitive to grammatical aspect and event duration in the context of a story continuation task. Overall this study demonstrates that grammatical aspect interacts with world knowledge to convey event structure information that influences how people interpret the end and beginning of events.