This is a qualitative exploratory study of the Green Brigade ultras of Celtic Football Club. Using mixed methods of semi-structured interviews, participant observation and desk-based research, it examines the group's activities, political culture, and experiences of policing. This study aims to provide a broad overview of the group, while also exploring areas such as policing and political culture in more detail. All interviews were audio recorded, transcribed verbatim, and analysed to uncover a variety of themes, amongst them key activities, policing, political education, anti-fascism, attitudes to sexism, and the influence of Irish Republicanism. The thesis draws upon theories of culture, subculture, social movements, radical pedagogy, ethnographies and studies of ultras, gender and football research, as well as studies of the Irish immigrant experience in Scotland, and specifically the role of Celtic as an expression of Irish identity. The Findings show a group with diverse political positions, but united under a common banner of anti-discrimination politics, and a broad commitment to Irish Republicanism. Within stadia, the highly visual elements of ultra culture are used to express these politics. Outside the stadia, the group undertakes various political activities, with an emphasis on inclusivity and grassroots organising. Criminalisation and policing feature prominently, with the group's activities with their collective culture being affected as a result. The implications of this study are several. It shows how a highly visible section of the Irish community in Scotland expresses a contentious sense of Irishness, and the consequences of this, both in terms of policing, and upon the group's culture. Questions of political organising, learning, discussion and outreach offer lessons to other groups and individuals involved in social activism. It is also offers an in-depth study of an ultra group, and contributes to the literature on this fascinating, and often highly political, subculture.