The thesis analyses British (Unison) and Swiss (Unia) strategies for organising Polish workers, focusing on projects delivered between 2008 and 2010 by Unison and between 2012 and 2014 by Unia. These projects were chosen because they were predominantly aimed at the inclusion of Polish migrants after the EU enlargement in 2004 and they involved aspects of policy implementation. Additionally, the thesis describes a successful strike of the mainly Polish care workers in Unia. The research analyses whether there were any gaps between the projects' aims and their implementation and what factors may have caused those gaps. The research is based on industrial relations theories applied in the context of comparative studies on migration: Penninx and Roosblad's (2000) theory that was adapted to the context of intra-EU migration with Marino in 2017 (Marino et al., 2017) and Connolly et al.'s (2014) and trade union revitalisation strategies (Frege and Kelly, 2003). The research argues that the internal dynamics of the unions, such as union identity and structures (Hyman, 2001; Frege and Kelly, 2003), were more instrumental in terms of project outcomes than the position of trade unions in the power structure of society, economic and labour market conditions or the social context. Overall, Unia was more successful and its approach was more sustainable. Unlike Unison, Unia had structures in place that supported the inclusion of Polish members (migrant workers' committees) and deployed resources to continue its organising efforts past the end of the project. The research shows that the provision of a dedicated resource is necessary to increase migrants' engagement in the union. Furthermore, as the analysis of the strike suggests, Unia was able to use the collective agency of Polish workers not only for their own benefit but also for the local workers employed in the care sector. Accordingly, this research suggests that Polish workers have a potential that could be used for trade union renewal.