Neuroscientists have long been working to understand how biological structures can produce the complex behaviors that are generated by the nervous system. However, even the basic operational principles governing a brain’s interconnected network of cells have remained painfully elusive. My laboratory is working on a scientific strategy focused on building a complete, multi-level picture of simple neural circuits that will advance our basic understanding of brain function and offers a complete view into the neuronal activity underlying a series of relatively complex behaviors. We are taking a first step towards this rather lofty goal via the comprehensive identification and examination of neural circuits controlling behavior in the larval zebrafish. This small and translucent vertebrate exhibits a series of visually induced behaviors which can be analyzed quantitatively down to the individual motor components. Using behavioral assays in combination with various calcium indicators and two-photon microscopy we monitor neuronal activity throughout the fish brain in an awake and intact preparation. An extended goal of our research is the study of how changes or variations in the behavior are reflected in changes in the underlying neuronal activity. To that end, we have developed several quantitative learning assays and tools for in vivo monitoring – and controlling – of neural activity in freely swimming larvae.