A motor vehicle headlight of the type comprising a single light source, a reflector including two zones suitable for generating two different respective light beams, a closure glass, and masking means situated in the vicinity of the source and capable of being displaced for selectively masking the light rays delivered by the source and propagating towards at least one of the two zones. According to the invention the two zones of the reflector are disposed side by side, each of them extending over the entire height of the reflector, each zone of the reflector is constituted by a portion of a reflecting surface sufficing on its own to generate the associated beam, and the masking means comprise at least one screen which, in its masking position, is situated to one side of the source.