The paper reviews the pyrolysis of biomass constituents and possible secondary reactions. Biomass pyrolysis yields mostly liquid and solid fuel, easy to store and transport. Relevant working conditions for experiments and large-scale operation are: (i) biomass particles < 200 mu m, (ii) a particle heating rate of at least about 80 K min(-1) and (iii) a reactor environment where the internal resistance to heat penetration is smaller than the external resistance to heat transfer (Biot-number, Bi < 1). The circumstances of TGA and DSC experiments meet these requirements and fully determine the reaction kinetics and endothermicity of the pyrolysis reaction. The reaction rate constant and the heat of reaction are essential parameters in the design of a pyrolysis reactor. For most of the biomass species tested, the first order reaction rate constant is large and >0.5 s(-1). The heat of reaction ranges from 207 to 434 kJ kg(-1). All results tie in with literature data, although the reader is cautioned in using literature data since experiments were not always performed under relevant testing conditions. (C) 2009 Elsevier Ltd. All rights reserved.