A light barrier having at least one transmitter (6) and at least one receiver (8) for a light beam and having a light path (1), which runs between a first side (2) and a second side (4) of a region to be monitored, can be produced flexibly and with little complexity by virtue of the transmitter (6) and of the receiver (8) being situated on the first side (2) and by virtue of the second side (4) containing an optical system (10) which picks up the primary light beam (7) emitted by the transmitter and which deflects the primary light beam (7) and returns it to the receiver (8) via the light path (1) to the first side (2) as a secondary light beam (9), which is separate from the primary light beam (7), at a distance from the primary light beam (7).