This chapter introduces the concept of primary preferences. Primary preferences are genetically inherited and direct individual choices toward activities that increase their chance for survival. In this process, beneficial factors (e.g., consumption of high-calorie food, sex) are associated with positive sensory and emotional responses, while disadvantageous factors (e.g., exposure to dangerous predators and extreme weather conditions) are associated with negative responses. These differences in responses allow individuals to rank all possible outcomes based on their level of attractiveness, which in turn defines a set of preferences over these outcomes. Since people cannot inherit the sensory responses associated with every single action, they need to explore their environment to discover what their primary preferences are. The chapter also provides a formal definition of exploration and exploitation. Exploration is any action that generates knowledge about certain aspects of the environment, while exploitation is any action capitalizing on knowledge already gained. On the one hand, because individuals have incomplete knowledge about the environment, they need to explore which actions earn high rewards. On the other hand, individuals need to exploit their current knowledge to obtain rewards. Since both goals cannot be achieved at the same time, people face a dilemma—the exploration-exploitation tradeoff.