This chapter delves into the technology of triboelectric nanogenerators (TENGs) based on solid-to-solid contact electrification (CE). We begin with an introduction to the two primary types of TENGs: AC-type and DC-type. The chapter then examines the five working modes of AC-type TENGs and the two material types used in DC-TENGs. Key aspects of performance optimization, material selection, environmental control, and charge excitation in solid–solid TENGs are also discussed. We then provide examples of TENG applications, emphasizing their potential as micro/nano power sources (e.g., from body motion energy, mechanical energy under in vivo conditions, vibration energy, and wind energy), self-powered sensors (including tactile, biomechanical, acoustic, human physiological, and chemical sensing), blue energy harvesting, and high-voltage sources. Finally, the chapter concludes with a forward-looking summary of future perspectives in TENG technology.