A solid fuel gasifier includes first wall structure (12) defining a gasification chamber (14) and means (50, 52) to collect particulate solid residue from gasification in the gasification chamber. Second wall structure (16) defines a gas combustion chamber (17) and means (19) is arranged for admitting a flow of hot gases from the gasification chamber to the gas combustion chamber as combustion takes place. Also provided is means (178, 170) to conduct hot gases from the gasification chamber and/or gas combustion chamber into thermal contact with said collected particulate solid residue, for facilitating post-combustion and/or post-reduction of the solid residue. Also disclosed are an agitator bed (52, 182) for fine particulate material, and a method of gasification of solid fuel.