To suppress the global temperature rise so as to avoid climate disasters it is necessary to shift to a renewable energy source. Biomass is the single most abundantly available renewable energy source that can be used on demand in direct combustion/gasification technologies. For a better understanding of solid biomass combustion, in the present chapter biomass fuels from different sources have been characterized in terms of physical and chemical properties, ash behavior and pretreatment methods, and suitable combustor types. Ash‐related issues relevant to the high alkali content typical of biomasses are discussed in detail. Effects of heating rate on pyrolysis product yields are compared for biomass and coal. For a better understanding of ignition/extinction characteristics of a solid fuel, the combustion kinetics for both volatile and char combustion with and without ash layer, with different shapes, are considered. Emissions during combustion of biomass, namely, NO
x
, SO
x
, HCl, heavy metals, and dioxins are described. Various combustion technologies are reviewed, from large‐scale entrained bed combustion systems to medium‐scale FBCs and fixed bed combustion. Finally, ash behavior in different combustion technologies is discussed.