Recent work in the field of second language (L2) motivation research has confirmed the crucial role of motivation in our behaviour or thought, incorporating all the factors that shape what we do or think (e.g., Dörnyei, 2020; Ushioda, 2020). With the development of complex dynamic systems in applied linguistics (Larsen-Freeman & Cameron, 2008), the L2 motivational self system (L2MSS) has strongly contributed to our understanding of how second language motivation is conceptualised and how this conceptualisation is related to a variety of learning and teaching phenomena. Research on the L2MSS has been extensive in recent years, calling for a meta-analytic examination. This study, therefore, reports a meta-analysis of studies that drew centrally on the L2MSS model. The meta-analysis examines the overall effect of motivation on language learning and addresses the relationship between the language motivation and variables that moderate its effectiveness. A total of 17 published studies, involving 18,832 language learners, were meta-analysed through calculating effect sizes for the effectiveness of motivation and for significant moderators. The results indicate a large effect of motivation on language learning. Further statistical analyses also reveal that various variables (including learner age, gender, educational level, learning context, target language, learning outcomes, and geographical locations) play a moderating role in the effectiveness of L2 motivation. Based on these findings, several directions for future meta-research within the domain of L2 motivation are charted.
