This comparative perspective opens up new angles for the discussion of currently debated issues such as the role of Universal Grammar in constraining development, developmental sequences in L2, maturational influences on the 'growth' of grammar, critical period effects for different linguistic domains, initial state and ultimate attainment in relation to length of exposure, and L1-transfer in relation to age of onset. These issues are explored using longitudinal, cross-sectional, and experimental data from L2 children acquiring a range of languages, including Dutch, English, French, and Greek.