"This bulletin is the first in a series of bulletins related to solid woody biomass fuels (solid biofuels). The information captured in the series is based on a suite of Solid Biofuel Standards developed and published by the International Organisation for Standardization (ISO). The bulletins are aimed primarily at consumers who are using or considering solid biofuels for space heating. The intent is to provide easy-to-read introductory guides to the use of solid biofuels. The series may also be of interest to fuel suppliers, equipment manufacturers, testing laboratories and regulators. This bulletin introduces sources of biomass, provides definitions for solid biofuels and their key characteristics."