International audience ; In this study, we describe the evolution of crop diversity in Flanders, using three indicators to measure diversity between crops and within crops: the Shannon index (H), the evenness index (E) - both used for diversity between and within crops - and genetic relatedness between varieties (CP). Despite the significant increase in the number of crops in Flanders, from 67 in 1950 to 101 in 2002, the results show a weak decrease in crop diversity between 1950 and 2002: H decreased from 2.52 to 2.50 and E decreased from 0.58 to 0.53. This apparent contradiction can be explained by the fact that the 'new' crops are mainly vegetables, which only have a small share in the total agricultural area, and thus hardly influence the overall crop diversity. The evolution of genetic diversity between varieties (within crops) from 1980 to 2002 is crop-specific. For maize, the number of cultivars with a high CP (Š 0.125) increased from 1.8 to 7.5%, indicating a decrease in genetic diversity. For potato and winter wheat the number of cultivars with CP Š 0.125 decreased (from 7.3 to 3.7% and from 6.9 to 6.0%, respectively), indicating an increase in genetic diversity within these crops, which is confirmed by the increase in the crops' H and E values.