Tweets by US President Donald Trump in 2017 brought Britain First – a former fringe political party better known for aggressively storming mosques – international attention. This chapter draws on original qualitative data and online materials to provide an overview of Britain First’s ideology, vigilante activities, and supporter base. Britain First’s vigilante activities, religious allusions, and savvy social media use set it apart from previous UK far-right parties and movements. In filming and uploading videos of its uniform-clad supporters storming mosques and distributing bibles, Britain First has threatened British Muslims, reached an audience of millions and faced increasing censure from technology companies and the legal system.