How do jihadists use the internet to learn bomb-making and other skills relevant for planning and executing terrorist attacks? This paper argues that jihadists may learn such skills through self-study, or through social interaction with other jihadists online. The first method, self-study, is most common, while the second method, via interactions, is a potentially powerful tool that jihadists have not yet exploited fully. In the last ten years, online training has changed in two major ways. First, the training material has become more pedagogical. This has made it easier for jihadists, especially lone actors, to learn terrorist skills through self-study. Second, interactive “training sessions” appear to be less common than before – at least on un-encrypted platforms. It is likely that interactive training still takes place via encrypted communication apps but in this field there is currently a gap in our knowledge. Thus, there is an urgent need for more research on how terrorists use encrypted apps for training purposes, and on how social media influences online terrorist learning in general.