The title of this textbook, Biosensors: From Electric Circuits to Immunosensors, implies that we are going to learn both electric circuitry (in relation to conventional sensors such as temperature sensors) and biosensors (such as antibody-based immunosensors). The idea of putting these two topics together into a single book came from my decision to add biosensor topics to the “Sensors and Controls” class taught at the University of Arizona. At that time, I realized there was no available textbook that equally addressed these two topics. In typical sensor textbooks, biosensor topics are relatively sparse. In biosensor textbooks, fundamental electric circuitry is rarely addressed. More importantly, none of those textbooks.