The construct of psychological flow bridges several areas of second language learning interest, including motivation, investment, self-efficacy, and autonomy. Flow, characterized by intense focus on an enjoyable activity that is at once challenging and accessible, creates conditions that have been linked to learning. Research interest in flow has grown, but the L2 research remains scarce and exploratory. This paper, which uses a two-study format, proposes and tests a new category coding scheme designed to explain which activities generate language-class flow. In Study A, third- and fourth-semester learners of Spanish, French, Italian, and German (N = 82) described their most flow-generating language-class experiences on an online questionnaire. In Study B, first- through fourth-semester students of Spanish (N = 588) did the same. The responses were coded to one category in each of four contrasting category pairs. Parallel analyses were conducted for each study, and within each study counts and chi-square tests were performed separately on each category pair. The results of both studies showed statistically significant contrasts within all four category pairs, and revealed that student-centered, open-ended, authentic, and non-competitive activities were more likely to generate flow than their opposites (i.e., teacher-centered, closed-ended, inauthentic, and competitive activities). Pedagogical implications and directions for future research are discussed based on these results.