This article provides evidence of critical factors of student retention in Language Massive Open Online Courses (LMOOCs). The study used multiple sources: tracked retention data (n=43,000), survey data in correlation with tracking data (n=400), and qualitative data (174 informants) from a survey (Friðriksdóttir, 2018, 2021a, 2021b). The data came from learners in seven courses and across different delivery modes in the LMOOC program Icelandic Online (IOL, https:// icelandiconline.com). First, analysis of the tracking data revealed low overall completion rates and that retention was highest in the blended mode of delivery. The analysis also uncovered a specific dropout pattern and pattern of user engagement. Second, the survey study identified six content-related and four tutor-related engagement factors and that learners' differing goals for course participation influenced retention. Finally, qualitative data analysis revealed intrinsic and extrinsic motivational factors responsible for course completion, whereas non-course-related factors affected retention among dropouts. Overall, the study identified multi-ranged determinants of student retention. [For the complete volume, "Intelligent CALL, Granular Systems and Learner Data: Short Papers from EUROCALL 2022 (30th, Reykjavik, Iceland, August 17-19, 2022)," see ED624779.]