Summary: The brain is a vastly interconnected information processing network. In humans, this network supports the rich mental space at the root of the imagination and enables many flexible cognitive abilities such as scientific and artistic creativity. How the brain implements these creative processes remains one of the greatest mysteries in science, and solving this mystery carries with it a possibility for deep understanding of human nature, human potential, and machine intelligence. Logie has proposed that a key substrate for human cognition is a "mental workspace" that enables mental representations such as visual imagery to be formed and manipulated flexibly (1). However, the neural basis of this workspace remains poorly understood, partially because existing experimental methods have limited ability to study complex, higher-order mental functions. Here we develop new methods to probe the structure and dynamics of the large scale networks underlying complex cognition. We use these methods to show that the mental manipulation of visual imagery is mediated by a fundamentally distributed network that spans structures throughout the human brain. Our findings conflict with dominant models that posit an anatomically modular basis for working memory and related processes. Instead, the component processes underlying the mental workspace appear to transcend anatomical modules, occurring at a level of organization that is fundamentally distributed across the brain. Rather than having a fixed anatomical basis, the mental workspace appears to be mediated by a core network that can dynamically and flexibly recruit existing cortical and subcortical subnetworks for specific tasks. These findings call for a shift in cognitive neuroscience research away from functional localization and localized neural circuits and toward the study of organizational principles that govern the large scale integration of information processing in the brain.