Tritium is a radioactive gas that is currently produced from dismantled nuclear weapons. The physics of how tritium works as a night sight is reviewed with a focus on the half-life of tritium. The decay rate of tritium is about 5 percent per year, which means that the radioactivity of the isotope has a half-life of about 10 to 12 years. As an officer’s tritium gun night sight grows older, the tritium loses energy and the night sight becomes dimmer. It is recommended that tritium night sights be replaced every 5 to 6 years. Most manufacturers of tritium night sights will replace the tritium inserts for a nominal fee. The remainder of the article reviews the six major manufacturers of tritium sights: AmeriGlo, Meprolight, Trijicon, TRUGLO, 21st Century Technologies, and XS Sight Systems. AmeriGlo manufacturers a comprehensive line of tritium sights that feature the company’s trademark Betalight tritium lamps. All AmeriGlo night sights carry a 12-year warranty on the illumination. Meprolight is an Israeli company that produces a variety of products for the military, law enforcement, and civil markets. Meprolight manufactures fixed and adjustable tritium sights that are suitable for almost all handguns used by law enforcement. Trijicon is the most well-known manufacturer of tritium night sights and was a pioneer in the design of battery-free, tritium-illuminated scopes and sights. Trijicon sights are among the best on the market and feature a tritium glass lamp installed in a small aluminum tube sealed with a polished synthetic sapphire crystal. TRUGLO is best known for its fiber-optic sights, but it also produces tritium sights and a new line of tritium fiber-optic (TFO) sights. The TFO is an innovative product that provides superior bright-light performance. 21st Century Technologies is one of the leading manufacturers of night sights; its P-T Night Sight is an extremely robust fixed system and its MMC sights offer the additional feature of adjustability. XS Sight Systems are favored for their unique design, which features a rear blade on the 24/7 that is a shallow V design with a small vertical tritium post, and their fast gun-fighting, self-defense capabilities in both daylight and low-light conditions.