Nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus. It is accompanied by the release or absorption of energy. See Wikipedia: Nuclear fusion.
Energy policy issues
There exist a wide consensus that the current methods for energy production are unsatisfactory in the long term, due to contamination, the greenhouse effect, diminishing resources, etc. In order to decide what energy generation methods should be used, the pros and contras of each method should be considered carefully.  Thus, making a policy choice in favour of one or the other energy option requires defining one's stance on:
- The importance of climate change and the impact of the burning of fossil fuels
- Quantitative estimates of the energy generation potential of each of the available energy options
- Estimates of global population growth and expectations regarding future energy demand, taking into account the rapidly rising energy needs of emerging economies
- The relative importance of the environmental impact of each of the energy options
- Social threats associated with each energy option: e.g., nuclear proliferation, or the threats associated with politically unstable energy supply regions
- The social acceptability of each energy option
- The relative economic cost of each of the energy options (contemplating the complete energy generation trajectory, including environmental damage and clean-up)
- Opportunities offered by the energy options in terms of, e.g., economic stimulation and employment
Making the correct choice requires studying each of these complex issues and somehow balancing the risks and opportunities involved. For some of them, the future evolution can be predicted with some confidence, but for others the predictions are hotly debated.
In any case, the choice for any specific energy generation options should not be considered in isolation from other global issues, such as the exhaustion of natural resources, poverty, and overpopulation, but rather as an element in the general framework of sustainable development, since all these issues must be addressed to guarantee the establishment of a stable and livable society. In particular, it is important to be aware that any technological solution to the energy problem (as well as to, e.g., agricultural production levels) will only mean temporary relief if population growth is not controlled. The latter issue should therefore receive top priority in any effort to attain sustainable development.
Whatever the case may be, energy generation in the near future will most likely be based on a mix of many options, that will vary in accord with local economic, environmental, and social conditions.
Energy generation in the future
As hinted at above, it appears desirable to significantly reduce our dependence on fossil fuels, due to the effect of the burning of fossil fuels on the global climate, contamination, and the accompanying loss of valuable resources (e.g., plastics).
What alternatives are available? A host of methods for energy generation exists that do not depend on fossil fuels. Among the primary such sources are wind energy, solar energy, and hydroelectric energy. Other sources, such as geothermal energy and wave energy, are and probably will remain quantitatively less important, or compete with food supply, as is the case with biofuels.
Hydroelectric energy is a potential 'base load' energy source, meaning that it is, or can be, available permanently and on demand. However, this energy source is only available at relatively few locations where the orography and climate is suitable.
Wind and solar energy are potentially plentiful, but strongly dependent on local weather. Therefore, they are not generally considered to be 'base load' energy sources, and can only serve to supplement other reliable energy sources. Energy generation should not be interrupted on a cloudy, windless winter's day! Combinations of various distinct power sources could mitigate this problem somewhat, but it is unlikely that it can be eliminated.
Nuclear fission power is an alternative that does not contribute to the greenhouse effect and serves as base load power supply, but suffers from problems associated with nuclear waste storage and processing, and public acceptance.
Therefore, the search for a base load power source for the future is still an unresolved issue. The discovery of a method to store energy on a large scale would completely change the picture, and enhance the viability of solar and wind energy; but currently, no such method is available.
Fusion as an energy option
Fusion undoubtedly offers some important advantages.  Once operative, energy supply would be virtually limitless; greenhouse gas exhaust would be zero; nuclear waste and the danger of nuclear accidents would be strongly reduced (with respect to fission power plants), and nuclear proliferation problems would be small or non-existent. On the other hand, there are complications due to the very complex technology required and the radioactive activation of the reactor vessel components. A significant part of the latter complications are due to the projected use of D-T fuels (deuterium-tritium) in the first-generation fusion power plants, which is the fuel that is easiest to ignite, but which leads to intense neutron radiation. One may speculate that, if successful, a second generation of fusion power plants can be developed that runs on other fuel mixtures (such as D-D), leading to a reduction of the problems associated with radioactivity.
Differing from some other energy options, the implementation of energy generation by fusion is not immediate, and subject to the solution of a number of technical problems. The current consensus is that while the technical challenges are formidable, they can be overcome. Thus, the main discussion regarding fusion as an energy option is not about its technical feasibility, but about the timescales for implementation.  While increased investment and improved focus of the current research efforts can certainly help to speed up progress, even under optimal conditions the time needed to achieve the first delivery of fusion-produced energy to the electricity grid is considerable, and it is unlikely that fusion can contribute to solving the short-term energy crisis (in the coming decades). Fusion must therefore be considered an energy option for the medium to long term.
- Energy development
- Intergovernmental Panel on Climate Change
- Climate change: A guide for the perplexed
- The American denial of Global Warming
- Population growth
- World Energy Outlook
- U.S. Energy Information Administration
- F.F. Chen, An Indispensable Truth: How Fusion Power Can Save the Planet, ISBN 1441978194
- C. LLewellyn Smith, Fusion Engineering and Design 74, Issues 1-4 (2005) 3-8