Starting with a brief review of the development of the circulating fluid bed (CFB) reactor principle, its main features as an important tool for efficient and thus environmentally acceptable processing of fine particulate solids, typically less than 150 mum diameter, are discussed. Various new industrial processes and high temperature process options starting with alumina calcination are described. Developing applications in the cement, metallurgical and chemical industries are approaching large-scale industrial importance. Efficient combustion or pressure gasification of fossil fuels and carbon-containing residues, fulfilling increasingly strict environmental legislation, is by far the most rapidly expanding field of application. In support of these developments our fundamental understanding of the fluid dynamics of CFB riser and of cyclone precipitation at high solid loadings has to be steadily improved. The reaction behaviour of aggregating fine particulate solids of varying size distributions also remains an open question.