Just like many social and technological networks, the brain is a complex system of interacting agents. A brain network typically exhibits properties that allow it to function efficiently, but also render it susceptible to disruption with minor perturbations. Our work is focused on defining and understanding the organization of functional and anatomical brain networks using human neuroimaging (e.g., Wig et al. 2011 Ann N Y Acad Sci). Specifically, we have developed tools to define areal networks at the level of individuals and also groups of individuals (e.g., Wig et al. 2013 Cereb Cortex, Wig et al. 2013 Neuroimage). This information is used in combination with social-network analysis tools to understand the complex relationships that exist between brain areas, determine how these relationships change across the adult lifespan, and understand the impact of these changes on health and cognitive function (e.g., Chan et al. 2014 PNAS).