In this brief, we discuss how posted and other hypermobile migrant construction workers suffer from marginalization in both the labour market and in access to social insurance, with variations between biographically different groups of posted workers. The brief is based on biographical worker histories of individual workers with varied posting experiences across the EU and sectoral expert insights from thematic focus group discussions. All data were collected under the rubrics of the SMUG project between May 2021 and March 2022 by research teams in Austria, Denmark, Finland, Italy, Poland, and Slovenia. The policy brief is written by the Finnish research team for the Finnish policy audience.