The Horsehead Nebula has been discovered in the visible range as a dark cloud appearing in extinction at the edge of a giant molecular complex in Orion. It is a photo-dominated region (PDR) illuminated by a massive star. It is of great interest to astrophysicists, as it is the ideal object for understanding the interactions between UV radiation emitted by stars and interstellar matter, the way radiation propagates inside dense clouds, and the impact of radiation on matter (photo-evaporation, ionization, dissociation, fragmentation, heating, etc.).