From producing elaborate bouquets of small molecules to regenerating entire tissues after injury, cells perform a spectacular array of complex behaviors. Yet, our ability to engineer similarly elaborate cell behaviors from scratch has proven both technically and intellectually challenging. By taking note of how evolution invents new cell behaviors and expanding the suite of non-neuronal optogenetic tools to precisely control molecular networks, I have developed a strategy for engineering natural cell behaviors in the same manner as evolution, instead of building new behaviors from the ground up. I will demonstrate this approach by exploring its application to controlling the metabolic network and the signal transduction network – two of the principle networks responsible for implementing a number of complex behaviors – across a range of model organisms. Additionally, I will show that in the process of discovering which inputs to cells – and methods of rewiring them – correspond to particular cell fates, I identified key organizing principles that will aid in the future development of designer cell behaviors.