By the late 1990s, several converging trends in economics, psychology, and neuroscience had set the stage for the birth of a new scientific field known as “neuroeconomics”. Without the availability of an extensive variety of experimental designs for dealing with individual and social decision-making provided by experimental and behavioral economics, many neuroeconomics studies could not have been developed. At the same time, without the significant progress made in neuroscience for grasping what is happening inside the brain when humans make decisions, primarily the use of functional magnetic resonance imaging, neuroeconomics would have never seen the light of day. In a more fundamental way, however, neuroeconomics has largely built on the fundamental knowledge developed by several branches of neuroscience for understanding brain functioning. The paper provides a broad overview of these neuroscientific foundations of neuroeconomics. It presents and discusses the main significant advances in the knowledge of brain functioning by neuroscience that have contributed to the emergence of neuroeconomics and its rise over the past two decades. These advances are grouped over three non-independent topics referred to as the “emo-rational” brain, “social” brain, and “computational” brain. For each topic, it emphasizes findings considered as critical to the development of neuroeconomics while highlighting some of prominent questions about which knowledge should be improved by future research. In parallel, it shows that the boundaries between neuroeconomics and several recent subfields of cognitive neuroscience, such as affective, social, and more generally, decision neuroscience, are rather porous.