The term “capacitance spectroscopy” encompasses a suite of measurements that inspect the charge responses of a device to various experimental controls such as temperature, frequency, time, and electric potential. These measurements yield useful information regarding the electrical properties of free carriers as well as bulk and interfacial electronic states energetically located in the bandgap. An incomplete list of extractable properties include carrier density, its dependence on the depletion width, the built-in voltage, interface charge, the energy level of in-gap states, their capture cross section, and density. In this chapter, we describe the concept of capacitance (Section 1.1), the related 4electric quantities, the associated physical phenomena, major types of capacitance in semiconductors (Section 1.2), and a survey of capacitance spectroscopy techniques in semiconductors (Sections 1.3 and 1.4).