Thermally stimulated current (TSC) is a short-circuit current which flows due to the displacement of charges in samples during heating. TSC measurement mainly evaluates two thermal relaxation processes: one is dipoles and the other is trapped charges. It is used in a variety of research fields, i.e., electronic devices such as diodes, transistors, and solar cells as well as dielectric, insulator, semiconductor, and ferroelectric materials. In this paper, we describe the fundamental of TSC measurement and the typical three applications. TSC enables us to observe the relaxation processes of molecular motions of plasticized and blended polymers. TSC also plays a crucial role in the evaluation of amount of charges and its stability in polymer electrets. Recently, defects of organic light emitting diodes (OLEDs) have been studied by TSC.