The global energy crisis is accompanied by the long-term interest of scientific and technological innovation. At the macro level, traditional fossil fuels such as coal, oil and gas are gradually being exhausted due to rapid industrialization and urbanization. Because of these characteristics, the search for clean and renewable sources of artificial energy is always a top priority of scientists to aim at sustainable development of the society. Since the introduction of triboelectric nanogenerators (TENGs) by Z.L. Wang group (2012), a wide range of nanogenerator designs have proven application potentials and unique advantages. TENGs have also demonstrated potentials in mechanical energy to electrical energy conversion by capturing many forms of ambient mechanical energy. The operation of TENG depends on the effect of electric friction, which induces static electricity between two material surfaces when being in contact. Therefore, TENGs are considered as a kind of "nanogenerators" due to their dependence on electrostatically induced nano-electrical friction and displacement currents during operation. In this paper, the fundamental theory, experiments, and applications of TENGs are reviewed as a foundation of the energy for the new era.