Recent conceptualizations of language learning motivation have highlighted its dynamic and contextual nature. Yet the role of the L2 learning context in shaping motivation remains under-explored. This study adopts an agency perspective to examine emerging motivational orientations across diverse medium of instruction settings. The present study reports findings from a motivation survey of 3854 secondary-school English learners across three types of instructional setting (English medium, Chinese medium and mixed medium) in Hong Kong. Hierarchical regression modeling points to a differential effect of motivation on language attainment across the three settings and the emergence of diverse internal structures of L2 motivation. Differences in the role played by agentic and nonagentic motivational orientations across the three settings are discussed and implications are outlined for theorizing language learning motivation and for language teaching practice.