Since 1976 the rate of utilization of fly ash from Danish power stations has increased from about zero to more than 75% of production. The main reason for this growth is the co-operation between the utilities and the fly ash consumers, i.e. predominantly the Danish and the Norwegian cement producers. This paper deals mainly with the precautions against separation, with storage and shipment of quality ash, and with the main principles of the co-operation between the producer and the consumer.