Altmetrics data are mainly gathered from readily available online sources, making altmetrics highly relevant in the context of Open Science. This report gives participants in the MLE on Open Science an overview of the different types of altmetrics currently being used or investigated for the purpose of research assessment, and their benefits and challenges. Based on a review of the situation in the Member States, it is clear that altmetrics are not yet being used for research evaluation purposes. Altmetrics hold a lot of promise, but it is too early to use them for research evaluation where funding decisions or hiring or promotion processes are concerned. More research is needed.