A beam combiner in a light scanning microscope for combining two illuminating beams that can be independently scanned. A first beam path (B1) guides a first illuminating beam (2) along a first optical axis (OA1) and a first optical device (L1) bundles the first beam (2) in an intermediate image plane. A second beam path (B2) guides a second illuminating beam (3) along a second optical axis (OA2) that intersects the first optical axis (OA1) at a point of intersection (Z) lying in or near the intermediate image plane, and a scanner (S2) for deflecting the second illuminating beam (3) and arranged before the point of intersection (Z) of the optical axes (OA1, OA2) in the propagation direction of the second illuminating beam (3). A coupling-in unit (4) is arranged at the point of intersection (Z) of the optical axes (OA1, OA2) and either has a mirror surface (5) having a passage opening (6; 7) at the point of incidence of the first optical axis (OA1), or is transparent except for a mirror element lying at the point of incidence of the first optical axis (OA1), wherein the size of the passage opening (6; 7) or the mirror element corresponds to the cross-section that the first illuminating beam (2) at the point of incidence and thus allows the first illuminating beam to pass or reflects the first illuminating beam, wherein the first and second illuminating beams (2, 3) propagate as a combined illuminating beam (8) after the coupling-in unit (4).