Intervention programmes for individuals who are showing signs of vulnerability to support for extremist ideologies, referred to as ‘secondary’ interventions in the field of public health, are core to countering violent extremism or CVE policy approaches. While governments attest to their success, there have been few publicly available evaluations due to the sensitivity of the data. As a result, secondary interventions are controversial and can raise the spectre of policing thought. This chapter argues that with the rise of extreme right and continued persistence of Islamist extremism, secondary interventions need to be a core part of efforts to counter extremism. Berger’s definition of extremism, based on social identity theory, provides a basis for reassessing our approach to secondary interventions. The chapter summarises existing evidence of different intervention types that could be applicable to secondary interventions and makes a number of suggestions for developing tactical approaches to interventions, as well as indicators for measuring vulnerability and success. It is argued that policymakers need to encourage the formalisation of a new field of ‘intervention science’ that combines and codifies knowledge across former extremists, social workers and mental health specialists. Finally, online interventions need to be explored in greater detail as social media presents opportunities for identification and engagement and are increasingly being used by intervention providersim.