Due to increasing consumption of food in the world and due to increasing cooperation of agriculture policy between European countries the importance of annual crop production estimation has been increased. Traditional methods for estimating crop production - methods based on statistics or representative farms - are not fast enough and new methods have to be developed. In Europe the Joint Research Center of the European Union has carried out the MARS -project (Monitoring Agriculture with Remote Sensing) in which the Crop Growth Monitoring System (CGMS) has been developed. CGMS is based on an agrometeorological crop growth model and a geographical information system.