Biomass is any living or recently living material which can function as a source for renewable, sustainable, useful energy. Examples of biomass "feedstock" are agricultural and forest residues, wastes from municipal or industrial sources, and crops grown specifically for energy purposes.

There are a number of advantages to using biomass as a source of energy:

• Biomass can be a source of consistent baseload power. This is in contrast to solar energy, which is intermittant, and wind, which is variable. Thus, biomass can augment both solar and wind to provide a steady source of sustainable energy.
• Biomass reduces waste disposal problems, when it is in the form of agricultural or forest residues (e.g. straw, small trees, undergrowth), municipal wastes or other material which would otherwise be thrown away.
• Biomass is a domestic fuel, providing improved energy security and countering dependence on foreigh sources of fossil fuels.
• Biomass, when gathered or harvested in a way which is renewable and sustainable, provides a "net zero" change in carbon dioxide, an important greenhouse gas.

The advantages of biomass are not, however, the full story. Like any good tool, the growth, gathering and use of biomass can be destructive, leading to both long-term economic harm and environmental damage.

• Excessive exploitation of forests for biomass fuels can disrupt a natural habit for wildlife, diminish the natural carbon sink that a forest provides, and add to greenhouse gases.
• Crops grown for biomass in place of food crops can make worse the plight of those reliant on imports of crops from food-producing countries.

Furthermore, the wide array of sources for biomass requires a variety of technologies and materials management processes to effectively and economically gather and convert biomass into useable energy.

These issues must be carefully considered and managed when venturing into the use of biomass for the generation of energy. The possibilities for good in biomass are substantial, but the possibilities for harm are present as well.

A fuel's energy density is a measure of how much energy can be released from a given volume of the fuel. For example, the energy densities of coal and gasoline are both much higher than that of wood, because wood contains about 50% water, plus a substantial amount of other materials which cannot be burned. Thus, the energy released from burning a cubic foot of wood is much less than that derived from burning a cubic foot of coal or gasoline.

Low energy density for biomass leads to problems in gathering and transporting sufficient amounts of it to locations where the raw fuel can either be burned or processed. Biomass tends to be bulky and inconvenient to handle, contributing to the expense and difficulty of using it as a source of fuel.