A standard system for grinding of Portland clinker to cement and the different principles for producing fly ash cement is described. The quality is influenced by the grinding system selected. The preferred system for intergrinding of fly ash and clinker involves introduction of fly ash into the finishing compartment of the mill. Efforts made to relate cement quality to specifications are described. Much attention is put on the physical characteristics of the fly ash: bulk weight, specific weight, particle distribution, particle shape, degree of agglomeration and colour. Surface areas and pozzolanic activity matter, but the air void content, which is much affected by grinding, is more important. This observation is based on testing of fly ashes and fly ash cements from production and laboratory grindings. The testing includes compressive strength, specific gravity, laser granulometry and SEM. The results have led to the introduction of new analytical and control procedures. A review of fly ash quality factors of most importance for cement producers is given. The energy balance in the production of blended fly ash cement involves savings from reduced consumption of clinker, and expenditure on transport, handling of fly ash and extra grinding of clinker and fly ash; net savings may be considerable.