Flow represents a state of complete involvement and heightened intensity that leads to improved performance on a task (Csikszentmihalyi, 1975, 1990). The notion of flow has the potential to provide worthwhile insights into the area of task engagement, yet the construct has received relatively little empirical attention by second language acquisition (SLA) researchers. This article uses flow theory to investigate the relationship between flow and engagement in second language (L2) use for inter-cultural and intra-cultural task-based interactions in a Japanese classroom for English as a foreign language (EFL) learners. The study employed a quasi-experimental design in which learners in the inter-cultural group (n = 18) and the intra-cultural group (n = 18) completed five dialogic, oral tasks. Tasks were then repeated, during which time the intra-cultural group continued to perform the tasks with Japanese peers, while the inter-cultural group performed the tasks with international interlocutors (n = 18). Analysis of flow questionnaires and task transcripts showed that inter-cultural contact had a significant positive effect on flow and one aspect of engagement in L2 use (turn-taking). In terms of the relationship between flow and engagement in L2 use, inter-cultural task interactions had a significant positive correlation between flow and turns. The findings are discussed in terms of two pedagogical implications: the provision of inter-cultural contact in language classrooms and the flow-enhancing potential of task design features.