Nearly 30000 Arabidopsis thaliana EST (Expressed Sequence Tags) have been produced by a French and an American consortium. Despite redundancy these sequences tag about half the expected Arabidopsis genes. Approximately 40% of the non-redundant EST can be assigned a putative function by simple homology search. This programme allowed the identification of a large number of genes which would have been very difficult to isolate by other classical techniques. It considerably stimulated many areas of plant biology by the rapid discovery a large number of genes, by revealing multigene families and by allowing the analysis of differential expression of the different members. Finally this programme facilitated construction of physical maps of the chromosomes and opened the way for complete sequencing of the Arabidopsis genome and comparative mapping of the major plant crops.