The longitudinal study “Multilingual Development: A Longitudinal Perspective” (MEZ) follows two cohorts of secondary school students with monolingual German, German-Turkish and German-Russian language backgrounds over the course of three years. The project investigates language-based, personal, and contextual factors that influence students’ multilingual development and examines how multilingual skills are related to other dimensions of educational success (e.g., transition decisions and processes in the educational system). The objective of MEZ is to identify starting points for developing strategies to increase young people’s chances for educational success.