Tritium, a radioactive form of hydrogen, plays a crucial role in the fusion experiments planned for the International Thermonuclear Experimental Reactor (ITER), currently under construction in southern France. Fusion, the process that powers the sun and stars, involves combining light atomic nuclei to produce energy. For ITER’s experiments, the preferred fuel is a mix of deuterium and tritium, two isotopes of hydrogen. While deuterium is relatively abundant and can be extracted from water, tritium is extremely rare and difficult to obtain. The world’s civilian stock of tritium is estimated to be only a few dozen kilograms, with ITER currently holding about 20 kg. To achieve its experimental goals, the reactor will need to consume approximately 14.5 kg of tritium, with additional amounts required for operational needs. Tritium is not a fuel that can be mined or extracted like traditional resources. It is naturally present in only trace amounts and has a radioactive half-life of about 12.3 years, meaning it decays relatively quickly. This makes it rare and difficult to maintain in large quantities over time. Because of its short half-life, tritium must be constantly produced, recovered, and stored. For fusion, this presents a unique challenge, as the fuel will need to be continuously replenished. The deuterium-tritium fusion phase, which is the core of ITER’s experiments, is now scheduled to begin in 2039, according to the project’s updated timeline, rather than the previously planned 2036. This delay allows more time to prepare for the complex logistics of managing such a rare and volatile fuel. Currently, most of the tritium available for civilian use comes from nuclear reactors that use heavy water, such as Canada’s CANDU reactors. In these reactors, neutrons produced during nuclear fission can convert deuterium in heavy water into tritium, which can then be extracted. However, the amount of tritium produced this way remains limited, and it continues to decay naturally over time. Unlike traditional resources, tritium cannot be stored indefinitely, making it a dynamic and difficult-to-manage fuel. This is particularly important as the world moves toward commercial fusion power, where reactors would need to produce their own tritium rather than rely on a global supply. ITER is designed to test the technologies that could enable this self-sufficiency. The challenge of tritium availability highlights a paradox in nuclear fusion. While the basic fuel—hydrogen—is abundant, one of the key isotopes required for the reaction, tritium, is extremely scarce. ITER’s success will not depend solely on its ability to generate fusion power but also on its capacity to demonstrate how future reactors can produce their own fuel. To achieve this, researchers are testing a method known as "tritium breeding," in which the neutrons produced by fusion reactions can be used to convert lithium into tritium. This process would allow future fusion power plants to generate the fuel they need, making the technology sustainable on a large scale. While ITER itself will not be self-sufficient in tritium, it will test the feasibility of this approach, laying the groundwork for the next generation of fusion reactors. The ability to produce tritium internally is crucial for the long-term viability of fusion energy, and ITER’s progress in this area will be a key indicator of the technology’s future potential.