Numerous studies established the role of the limbic system in fear and reward: it integrates sensory information, encodes emotional states and instructs other brain centers to regulate physiology and behavior. The limbic system, however, consists of many distinct and highly interconnected neuronal populations. Resolving how emotions are processed in this network at the level of single neural circuits remains a major challenge.As entry point into the complexity of emotion circuitry, we propose to study, in exemplary fashion, how fear, as the most basic paradigm for emotions, is processed in key limbic hubs. Genetic manipulation of brain circuitry with electrophysiological methods and Pavlovian conditioning in mice, are powerful tools to explore which and how individual circuits in these hubs control emotional states, and, in turn, how genes and psychoactive drugs modulate circuit activity, emotional states and behavior.We envision this ERC funded research to uncover general principles of the network organization of both emotions and behaviors. It is our hope that we contribute useful tools and methodological framework for investigating other brain functions in a similar manner.