IMGT, the international ImMunoGeneTics information system (http://imgt.cines.fr), is a high quality integrated knowledge resource specializing in immunoglobulins (IG), T cell receptors (TR) and major histocompatibility complexes (MHC) and related proteins of the immune system (RPI) of human and other vertebrates, created in 1989 by LIGM at the Université Montpellier II, CNRS, Montpellier, France. IMGT provides a common access to standardized data which include nucleotide and protein sequences, oligonucleotide primers, gene maps, genetic polymorphisms, specificities, and 2D and 3D structures. IMGT includes five databases (IMGT/LIGM-DB, IMGT/3Dstructure-DB, IMGT/MHC-DB, IMGT/PRIMER-DB, IMGT/GENE-DB) Web resources ('IMGT Marie-Paule page') and interactive tools (IMGT/V-QUEST, IMGT/JunctionAnalysis, IMGT/PhyloGene, IMGT/LocusView, IMGT/GeneView, IMGT/GeneSearch, IMGT/StructureQuery). IMGT data are expertly annotated according to the rules of the IMGT Scientific chart based on IMGTONTOLOGY. IMGT tools are particularly useful for the analysis of the IG and TR repertoires in physiological normal and pathological situations. IMGT has important applications in medical research (autoimmune diseases, AIDS, leukaemias, lymphomas, myelomas), biotechnology related to antibody engineering (phage displays, combinatorial libraries) and therapeutic approaches (graft, immunotherapy). IMGT is freely available at http://imgt.cines.fr.