Novel structural and functional techniques have allowed in vivo analysis of large, distributed brain networks. Probing the systems or network level has been of particular interest in the field of neurodegenerative disease as it has become increasingly clear that degenerative diseases target large-scale brain networks. Task-free functional MRI (TF-fMRI) is a particularly appealing technique since it is safe, requires minimal patient cooperation (important in diseased populations), can be performed on most commercial MRI machines, and results in data that can be shared between centers easily. In this chapter, we provide a brief introduction to TF-fMRI, including the principles underlying the BOLD signal, image preprocessing, and data analysis. We then review age-related connectivity changes before moving on to Alzheimer’s disease, which is our primary focus within the dementias. Following this, we briefly review alterations in function connectivity in non-Alzheimer’s dementias. Finally, we discuss the future of functional connectivity in neurodegenerative research and clinical practice.