Interest in biomass fuels is increasing worldwide to produce heat, power, liquid fuels and hydrogen with reduced greenhouse gas emissions. Thermochemical biomass processes are relatively well developed, e.g. for direct combustion, gasification and pyrolysis. However, critical problems often arise when attempting to feed biomass into reactors, preventing continuous operation of the entire system. Although biomass feeding has received some attention in the past and several novel feeders have been patented, most feeders are fuel-specific and unable to provide reliable, efficient and economical feeding, especially for herbaceous fuels and reactors operating at elevated pressure. The most common feeding problems are bridging, rathole formation, blockage, seal failure and reactions in the feed line. The present study identifies the biomass properties which influence feeding and reactor performance. Design principles and selection of feeders are also covered. We summarize experiences and failure potentials of biomass feeding for combustors and gasifiers, as well as providing an overview based on reported feeder experiments, useful for later study of biomass utilization. (C) 2012 Elsevier Ltd. All rights reserved.