Online behaviour can provide a unique window from which we can glean intent. From an intelligence standpoint it provides an important source of open-source information. However, making inference of intent from online activity is inherently difficult. Yet elsewhere progress is being made in incorporating information online into decisions regarding risk and offender prioritisation. This chapter synthesises lessons learnt from studies of risk assessment of violent extremists, risk assessment online, and the form and function of extremist materials online in order to begin to approach the issue of online risk assessment of violent extremism. In doing so it highlights issues associated with the diversity of online extremist behaviour, the diversity of offline extremist behaviour and the general lack of understanding related to the interaction of online and offline experiences, and how this contributes to the wider psychological process of ‘radicalisation’. Implications for practitioners are discussed.