Grammatical aspect is a linguistic correlate of the temporal distribution of an event. However, aspect is not identical across languages. Crosslinguistic differences in mapping between aspect and basic temporal features such as event stage can reveal underlying language-specific criteria that guide event conceptualization. We investigated the relationship between grammatical aspect and event stage in conceptualizations of in-progress and completed events by native (L1) and non-native (L2) speakers of aspectual languages Russian and English. In L1, event stage predicted aspect in Russian but not in English. In L2s, event stage did not predict aspect. We discuss these findings in terms of crosslinguistic differences in the relevance of event stage for conceptualization in L1 as well as the role of L1 transfer in L2 aspect use.