Tritium is produced in light water reactors from various sources and the design source terms for both BWR and PWR plants are reviewed. The chemical forms of tritium produced in the coolant are discussed in terms of water radiolysis and free radical reactions in the reactor core regions, and the major form of tritium released from the coolant systems is confirmed to be tritiated water. The tritium activity concentrations and inventories in various coolant systems have been measured, and the release pathways of tritium from nuclear power plants are also reviewed in this paper. Decreasing trends of tritium release from nuclear power plants in both liquid waste and ventilation sources have been observed in Taiwan. The impact of tritium release on environmental radiation is estimated with well-established screening models, and the results confirm that the impact is less than 1% of the regulatory limits and less than 0.1% of the natural radiation background.