This retrospective review applies a language socialisation perspective in examining the findings of a four-year research project on Swedish immersion in Finland. Findings from nine sub-studies within the project are reported with a point-of-view from three key actors’ (teachers, students, and parents) language socialisation processes. Results show that a special feature of immersion teacher socialisation is its continuous attention toward the additive multilingual nature of immersion education, which requires sustained attention to multilingual language use and development. Students in Swedish immersion are socialised into the use of multiple languages in school and act as socialisation agents also outside school. They bring the immersion language to their homes and influence the family language use. Immersion may thus have a considerable influence on how majority language speakers self-identify as language users. Altogether, the sub-studies demonstrate that the benefits of immersion education extend well beyond learning success of students.