The electroencephalographic signal, or EEG, is a peek into the workings of the human brain. Because obtaining the EEG is relatively inexpensive, it is a very useful diagnostic tool in low-resource environments. With the development of mobile implementations, it has the potential to provide insights into the workings of the human mind outside of laboratory conditions. To understand the EEG and use it, we need to have some basic understanding of the organ generating the signal—the brain. The brain is the most complex entity known to humans. With about 86 billion neurons, which can have up to tens of trillions of connections, the intricacy and complexity of the brain are beyond comprehension. The only way we can begin to get a handle on it is by simplification and gross generalizations. So, let’s proceed to do just that. We can think of the brain in “evolutionary” terms, popularized in the idea of a triune brain [48] by Paul Maclean in the 1960s. In his formulation, we can divide the brain into three parts: a lizard brain, or reptilian complex, enclosed in a paleomamalian complex, which is enclosed in the neomammalian complex.