Smoke emissions from wildland fire can be harmful to human health and welfare, impair visibility, and contribute to greenhouse gas emissions. The generation of emissions and heat release need to be characterized to estimate the potential impacts of wildland fire smoke. This requires explicit knowledge of the source, including size of the area burned, burn period, characteristics and condition of the fuels, amount of fuel consumed, and emission factors for specific pollutants. Although errors and uncertainties arise in the process of estimating emissions, the largest errors are related to the characteristics of the fuels and amount of fuel consumed during the combustion phase. We describe the process of characterizing emissions and review the knowledge and predictive models currently available for performing the calculations. The information can he used by scientists, regulators, and land managers to improve the approach needed to define the emissions source strength for improved air quality and impact assessments.