Understanding and characterizing the relationship between mental phenomena and the brain is a huge challenge for modern neuroscience. No doubt, the conservative orthodox view of this relationship can be described as physicalist. Physicalism is the idea that, no matter how enigmatic mental phenomena may seem, they are nevertheless completely describable in physical and material terms. Still, despite centuries of effort, aspects of mind, such as the qualitative nature of subjective experience, have defied physical characterization. In the early 1920s, emergentism was advanced to explain the relationship between physical reality and higher-order phenomena, including life and mind. According to emergentism, such higher-order phenomena are derivative of and, at the same time, autonomous to underlying physical reality. This article describes the historical and philosophical development of emergentist theses, particularly as they have been treated in the neurosciences.