Nuclear fusion is a process by which two atomic nuclei collide together to form a heavier atomic nucleus. For example, two nuclei of Hydrogen may collide to form a nucleus of Deuterium: this is the first step of a chain of nuclear reactions that occur inside the Sun. Nuclear fusion reactions of light nuclei typically produce energy; for example, for the H+H reaction inside the sun, the mass of the final nucleus of deuterium is less than the mass of the initial nuclei. The difference in mass is released as energy according to the famous Einstein's equation E=mc^2. Nuclear fusion of heavier nuclei (iron and above) instead requires energy. These nuclear rections typically happen in nature only in extreme astrophysical events, such as supernova explosions. Nuclear fusion is seen by many as a possibility to solve the World's energy crisis. If we could achieve a controlled fusion reaction, energy could be extracted through heat in fusion reactors similarly to what happens in existing fission nuclear plants. However, nuclear fusion would not produce radioactive waste, thus solving much of the people concerns about nuclear plants. Research and development is underway across the globe to develop a commercially viable and sustainable nuclear fusion energy production.