A microscope which makes possible a spectrally-flexible excitation and detection of fluorescence in an economical manner. For this purpose, means for frequency conversion are arranged in the common beam path and a filter for excitation light is arranged in addition to the main beam splitter in the detection beam path. The frequency conversion achieves a spectral delimitation between illumination light, which is emitted by the light source, and excitation light which brings about fluorescence excitation in the specimen. Because the frequency conversion takes place in the common beam path after the main beam splitter, it is possible for both a spatial separation of illumination light, and excitation light and fluorescent light (detection light) emitted by the specimen, to be carried out in an economical manner at the main beamsplitter according to spectral bands because of the spectral difference between illumination light and excitation light.