This handbook is an edited and updated version of the final report of the IEA Bioenergy sponsored Pyrolysis Activity - PYRA - that officially finished in 1998 and accomplished many valuable contributions to the science and technology of fast pyrolysis. It is intended that this handbook will provide a useful guide both to newcomers to the subject area as well as those already involved in research, development and implementation. The IEA Bioenergy Pyrolysis Task is continuing this work as a collaborative project with the European Commission network on fast pyrolysis of biomass which is now known as PyNe. The European Network was first formed in 1995 as an EC sponsored project in the AIR Programme (AIR3-CT94-1857). At the end of the three-year lives of the Networks in 1997, both sponsoring organisations recognised the benefits from their integration. This led to the present PyNe Network, which is co-sponsored by the European Commission FAIR Programme (FAIR-CT97-3409) and IEA Bioenergy, and which itself is sponsoring the publication of this book as a contribution to the technology.