This systematic literature review provides an overview of research and practices that have occurred over the last five years in the realm of adults learning mathematics through online learning. It includes research in the tertiary space, much of which has focused on university education. Systematic literature reviews are a method of making sense of large bodies of information and are a method for 'taking stock' and understanding of the evolution of a field of inquiry. The review found that there have been three main streams of research in the literature on adults learning mathematics online. The research in these three streams is summarised and discussed. From the review it is apparent that in the context of adults learning mathematics, there is a dearth of research on online learning in general; while there are studies that have examined the use of certain technologies, there is less of a focus on the online learning context for adults learning mathematics. Recommendations for areas of research are provided.