This article is presented to discuss general combustion and emissions issues with biomass co-firing, as well as specific issues with particular biomass fuels, such as fouling. The tests of co-firing were carried out in a lab-scale bubbling fluidized bed combustor. Biomass is an attractive and sustainable renewable fuel to supplement coal combustion in utility boilers. Coal and biomass fuels are quite different in composition. Ash composition for the biomass is fundamentally different from ash composition for coal. Chlorine in the biomass may affect operation by corrosion. Ash deposits reduce heat transfer and may also result in severe corrosion at high temperatures. Biomass and coal blend combustion is a promising combustion technology; however, significant development work is required before large-scale implementation can be realized. Coal co-firing was successful with up to a 20% biomass mix boilers. Issues related to successful implementation of coal biomass blend combustion are identified. Co-firing of coal and biomass is an effective method of control NOx. Formation of NOx decreases with the increase of biomass fraction. This study focuses on five of the critical fireside issues associated with co-firing: ash deposition, SO2 emission, NOx formation, corrosion, and carbon burnout.