It has become widely accepted that emotions play a key role in the learning process. Therefore, understanding learners’ emotions in computer-assisted language learning (CALL) has become an important area of inquiry as the demand for these resources continues to increase. To date, however, research has focused almost exclusively on one emotion, anxiety. Consideration of a much broader range of both positive and negative emotion would provide a more holistic insight in to the online language learning experience, and thus warrants further investigation. This research, presents an investigation in to the emotional experiences of learners participating in an Irish language, massive open online course (MOOC). Language learning MOOCs (LMOOCs) such as this one constitute an emerging and relatively unexplored CALL environment that has much to gain from emotion research. Using Pekrun’s (2006) Control-Value Theory of Achievement Emotions as the guiding theoretical framework, this study seeks to answer the over-arching research question: What are the sources of learners’ emotions experienced during an LMOOC? The research design adopted to address this question was iterative in nature with findings from prior stages contributing to the methodological instruments and procedure used in the main study. An experience sampling method was adopted to collect self-report data pertaining to learners’ emotions and their cognitive appraisals during the main study. This approach facilitated in-the-moment emotion reports from participants following various task-types and tested the Control-Value Theory at an intra-individual level. This data was further enhanced by weekly emotion diaries, which delved deeper into the learners’ perspective. This multiple methods study finds that learners experience a range of both positive and negative emotions while learning the Irish language online. A multilevel analysis of the quantitative data confirms that the cognitive appraisals of perceived control and subjective value both directly and interactively predict learners’ emotions at an intra-individual level during the MOOC. Furthermore, there are significant relationships that exist between task types and learner emotions, a finding that is of particular relevance to learning design and pedagogical strategies. A thematic analysis of the qualitative data supports these quantitative findings but also highlights other appraisals that appear to be relevant to the elicitation of emotions during the LMOOC. Taken together, the findings of this study suggest that learning a language online is not just a cognitive process but also an emotional one and educators, learning designers and even the learners themselves need to consider this when engaging in such courses.