Recent genomic studies have led to an inventory of the genes encoding their immune receptors. Some have been submitted to great diversification by duplication in the germline. In some families like LRR and IgSF several species of vertebrates and invertebrates diversify further the receptors by individual somatic processes demanding cellular control and selection that can lead to the genesis of adaptive systems. At all levels many convergences reveal even better than conservations the intensity of pressure exerted on the immune systems to diversify their immunoreceptors in front of the changing environment.