The biology of corticotropin-releasing factor (CRF) finds increasing interest in the scientific community because of the neuromodulatory actions of CRF on brain functions such as learning, anxiety, feeding, and locomotion. Additional actions on immunumodulation and apoptosis have recently been discovered. All actions of CRF are mediated by G protein-coupled receptors, which trigger different, sometimes opposite actions in different regions of the central nervous system. The CRF system exhibits considerable plasticity by the involvement of numerous different ligands, splice variants, and transductional couplings. The generation of multiple splice variants is facilitated by the intron exon structure of the CRF receptor genes.