The gilthead sea bream, Sparus aurata, a euryhaline Sparidae, occurs in the Mediterranean, the Black Sea and in the Eastern Atlantic. At present, the gilthead sea bream is one of the species of major economic interest in the Mediterranean. In addition, belonging to the order Perciformes, an order that underwent an explosive radiation 60 mya, it is of key interest for evolutionary studies. As a result of commercial interest and technological development in aquaculture an increased need of understanding its biology at molecular level is fundamental. The present book describes the accumulation of solid genomic information in sea bream in form of ESTs, gene expression data and RH map plus first comparative mapping approaches. It also shows functional studies of genes resulting from the established molecular tools. This work aims to give an introduction for students as well as scientists towards the construction and application of molecular tools for non-model organisms like marine fish species with scarce genomic information. It further seeks to show the significance working with non-model fish species taking into account the diverse physiology of Teleosts.