Despite major advances in understanding the properties of single cells and molecule-level processes, how the cerebral cortex operates at the circuit level continues to remain mysterious. For the past several decades, neuroscientists have observed remarkable regularity in the neural architecture: cortical areas communicate through feedforward, lateral, and feedback connections. Clearly, understanding the functional principles of cortical communication is key to understanding how the entire cortex operates. My laboratory has embarked on a quest to understand the principles behind the network encoding of sensory information and executive control in cerebral cortex. Our long-range goal is to understand the mechanisms underlying state and experience-dependent changes in the function of cortical populations and how the coordination of distributed networks of neurons influences behavior. To accomplish these goals, we combine electrophysiological (multi-electrode recording in restrained and freely moving non-human primates), optogenetic and electrical stimulation, behavioral approaches, and computational methods. Our basic strategy is to help develop new tools for modulating and recording population activity across cortical circuits in restrained and unrestrained animals and then apply these techniques to examine the neural computations and coding principles across cortical circuits.