I will describe studies of the neural bases of cognitive processes. Rodents, mostly rats, are trained to perform behaviors that lend themselves to quantitative modeling that can help identify and assess specific cognitive processes, such as decision-making, short-term memory, planning, and executive control. With these well-quantified behaviors in hand, we then use electrophysiological recordings, optogenetic perturbations, and computational modeling. We aim to understand the neural architecture underlying cognition, across multiple levels, from local neural circuits, to interactions between brain regions, to overall behavior.