The L2 Motivational Self System (L2MSS) has strongly contributed to current understandings about the conceptualization of language motivation and the interconnections between L2 motivation and maximized learning outcomes.Research informed by the L2MSS has been extensive, and is on the increase. The accumulating body of empirical work in this area calls for meta-analytic and synthetic assessments. Situated within the L2MSS framework, the present meta-analysis examines the overall effectiveness of L2 motivation on language learning and addresses the relationship between L2 motivation and variables that moderate its effectiveness. A total of 17 published studies, involving 18,832 language learners, were meta-analyzed through calculating effect sizes. The results indicate a large effect of L2 motivation on language learning. Moderator analyses also reveal that the overall L2 motivation construct is multifaceted, and its effectiveness is constituted and shaped in interaction with learner age, gender, educational level, learning context, target language, learning outcomes, and geographical locations. From this basis, we contextualize the findings, discuss implications, and consider areas for further work on L2 motivation.