We have used biomass energy or "bio energy"—the energy from plants and plant-derived materials—since people began burning wood to cook food and keep warm. Wood is still the largest biomass energy resource today, but other sources of biomass can also be used. These include food crops, grassy and woody plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes. Even the fumes from landfills (which are methane, a natural gas) can be used as a biomass energy source.

Biomass, in the energy production industry, refers to living and recently living biological material which can be used as fuel or for industrial production. Most commonly biomass refers to plant matter grown for use as bio fuel, but also includes plant or animal matter used for production of fibres, chemicals or heat.

Biomass is grown from several plants, including switch grass, hemp, corn, willow and sugarcane. The particular plant used is usually not very important to the end products, but it does affect the processing of the raw material.

Though biomass is a renewable fuel, it can still contribute to global warming. Biomass is part of the carbon cycle. Carbon from the atmosphere is converted into biological matter by photosynthesis. On decay or combustion the carbon goes back into the atmosphere. This happens over a relatively short timescale and plant matter used as a fuel can be constantly replaced by planting for new growth. Therefore a reasonably stable level of atmospheric carbon results from its use as a fuel.