Usage-based theories have stressed the importance of input for language learning both in and outside the classroom. When large amounts of input are available, learning gains can be rapid and large. However, the actual learning processes driving L2 development remain to be addressed. Throughout this project, I will look into L2 English speaking development of young, adolescent learners both at the group level and the individual level. An approach which has foregrounded the learning process is complex dynamic systems theory (CDST). When considering the individual learner, I will also investigate the data from a CDST-perspective. I will study L2 English speaking development in two time periods: one long-term study (across secondary school) and one intensive longitudinal study investigating ‘real-time’ development (one-year study). The project will focus on several aspects of the learning process: - First, I will investigate the shape of the learning curve(s) both at the group level and at the individual level. - Second, I aim to study different aspects of language proficiency and I will look into the relationship between complexity, accuracy and fluency in young learners’ L2 English speaking development. - A third issue under investigation is the contribution of internal and external resources to L2 English speaking development. With this longitudinal investigation I wish to contribute to our understanding of the L2 language learning process.