Cotton fibers are the premier natural fibers for textile production. The two tetraploid species, Gossypium barbadense and G. hirsutum, differ significantly in their fiber properties, the former having much longer, finer and stronger fibers. A better understanding of the genetics and underlying biological causes of these differences will aid further improvement of cotton quality through breeding and biotechnology. In the recent period, the availability of a genetically stable interspecific RIL population (140 F2:8 individuals) allowed CIRAD, Bayer Crop Science and CSIRO, to benefit from the financial support of the French National Research Agency (ANR) for a project named "genetic and genomic dissection of cotton fiber quality". The genetic map of the RILs (800 loci, 2044 cM) and more importantly the consensus map resulting from its integration with the BC1 map (75 BC1 + 140 RILs, 1745 loci, 3637 cM) now constitutes one of the best basis internationally, as it offers a maximized number of bridge loci in common with other interspecific G hirsutum x G barbadense maps (TAG, 2009, 119:281-292). The phenotypic characterisation of the fibers of the RILs on 4 continents and several growing seasons generated 11 independent fiber data sets which served for QTL mapping. The 167 significant fiber QTLs (LOD>permutation based threshold) and 651 putative LOD peaks (LOD>2) from these RIL experiments were integrated with QTLs from the BC1 and from the literature. The meta-analysis of this large set of QTL data using MetaQTL software indicated that some chromosome regions hosted "confirmed" QTLs. An effective co-localization of unidirectional (similar sign of additivity) LOD peaks from at least 5 independent data sets was observed in at least 26 cases (a given fiber trait and a given chromosome region) where meta-clusters of QTLs were defined (BMC Plant Biol, 2010, 10:132). The fiber trancriptomes of the 2 parents and of a set of 88 RILs were analyzed with focus on 2 key develo