The overall aim of this dissertation is to gain a deeper understanding of pedagogical collaboration among mainstream teachers, special educational needs teachers, mother tongue teachers and multilingual study guidance tutors when supporting multilingual students' language and knowledge development in Swedish primary schools. The dissertation consists of a licentiate thesis, (Study I), two articles (Study II and Study III) and this introductory chapter, “kappa”. Study I, an ethnographic case study, was based on sociocultural perspectives (Vygotsky, 1999) in the design, collection, analysis, and discussion of data, which consisted of observation, interviews, informal conversations and other collected information about the class. In studies II and III, Bronstein's (2003) systematic literature review provided insight into influencing factors on interdisciplinary collaboration and was used in the analysis. Studies II and III, consisting of 13 in-depth interviews with mother tongue teachers/multilingual study guidance tutors teaching in 15 different languages. In this “kappa” the results of the three studies are synthesized by dint of Bronstein’s influencing factors on interdisciplinary collaborations. Thereafter, the results are discussed by utilizing sociocultural theories on teaching and learning as well as on recent research on pedagogical collaboration. The results of the analyses show that the collaboration between teachers, SEN-teachers and mother tongue teachers is mostly affected by structural characteristics. Besides structural characteristics, the collaboration between teachers, SEN-teachers and multilingual study guidance tutors is influenced by the perception of a tutor’s professional role, tutors’ and teachers’ personal characteristics as well as the history of collaboration. The findings indicate that the pedagogical collaboration between teachers, SEN-teachers, mother tongue teachers, and multilingual study guidance tutors could be significantly improved if better structures were created at policy level to facilitate the organization of pedagogical collaborations. Valuable pedagogical collaboration time could then focus on supporting multilingual students' language and knowledge development instead of solving practical or organizational matters. A more structured organization could also contribute to building a more sustainable future for pedagogical collaboration that is more holistic and responsive in relation to multilingual students’ needs.