In the framework of an interactive/action research project the overall aim of this study is to describe and analyze how teachers negotiate professional identities in compulsory school. The aim is also to describe and analyze teachers’ learning and development of knowledge in the project. The central research question is: How and about what do teachers negotiate professional identities in different communities of practice? The results of the study show that teachers negotiate professional identities in a flexible expanding multimembership of communities of practice. As brokers of information and knowledge between and within communities of practice at school, and from various identity positions, the teachers negotiate overlapping identities. Memberships in communities for adults only are growing in relation to teachers’ work regarding the entire work situation. The study’s main conclusion is that teachers in the new era negotiate identities within a web of tensions between fragmentation and coherence of the complexity of the work in its entirety through the multimembership in communities of practice. The study proposes that an awareness of complexity is fundamental, and that such an understanding can be enhanced by the teachers by developing themselves as brokers and by their reification of boundary objects within a complex multi-membership.