Nuclear fission is the splitting of the nucleus of an atom, which releases an enormous amount of energy and radiation. This is what is used in nuclear bombs and energy plants.
Nature’s fusion, the merging of nuclei, is the opposite process. This is actually the same process taking place within the Sun and stars. The obstacle has been generating enough heat here on earth to accomplish this process. Cold fusion is the dream of creating this process at room temperature. Nonetheless, there are MANY companies involved in developing hot fusion here on Earth, and if accomplished, will mark the end of fossil fuels and the cost would be infinitely smaller. This could be the next major innovation that spurs a leap forward in the economic progress of humankind.
Before we see fusion technology in use, we are probably looking at the next wave in 2024-2028. Keep in mind that if this technology is accomplished, it would profoundly change everything.