This TIP provides basic information on nitrogen oxide (NOx) formation and control technologies. After years of limited interest in applying NOx regulations on industrial boilers that fire biomass derived fuel (hog fuel, bark, wood chips, saw dust, sander dust, railroad ties, pulp mill clarifier sludges, construction and demolition debris, and red and black pulping liquors), regulators in some states are establishing NOx emissions limits on boilers that are strict enough to impact boiler operations. Informed decisions on fuel usage, operating parameters, NOx control technology implementation, and impact on other pollutant generation will be needed. This TIP offers background information to help engineers, operating staff, and managers understand the issues and the options that are available to meet compliance requirements.