This volume explores the cognitive neuroscience of second language acquisition from the perspectives of critical/sensitive periods, maturational effects, individual differences, neural regions involved, and processing characteristics. The research methods used include functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and event related potentials (ERP). The studies in this volume provide initial answers to core questions including: which brain areas are reliably activated in second language processing? Are they the same or different from those activated in first language acquisition and use? And what are the behavioral consequences of individual differences among brains?