How does our experience with language impact human brain organization? In this session, I will focus on our research spanning three decades in which we combine behavioral methods with functional neuroimaging (PET and fMRI) under different language learning scenarios, to investigate how the brain is influenced by the age of acquisition, proficiency in the language, and the distinctive characteristics of languages. I will also discuss the use of anatomical techniques such as voxel-based morphometry (VBM), cortical thickness measures, diffusion tensor tractography, and resting-state MRI to enhance our understanding of the critical-period phenomena and neural plasticity in the human brain. This program of research addresses questions about the capacity of the human brain to change as a result of learning. I will talk about the extent to which neural patterns are fixed and the extent to which these patterns can be altered later in life as a result of experience. The results of these studies reveal the neural underpinnings of human brain development in relation to the age of language exposure, and they suggest periods when learning language are most optimal. I will also discuss longitudinal studies and how these can be used to study language learning, neural biomarkers for language learning and brain plasticity in response to learning. Finally, I will introduce new tools we are developing using speech samples to understand how our brains change in health and in disease, specifically with a focus on using speech as a window into diagnosing neurological disease.