The wealth of optical phenomena offers various new opportunities for selective interaction with the world of nanometer dimensions if the relevant radiation fields can be sufficiently confined, for instance by small apertures in an opaque screen. Many optical effects manifest themselves in a novel way, having strong similarities to microwave antennas and waveguides. Scanning near-field optical microscopy, which dwells on these principles, allows the diffraction limit to be broken and optical images with a resolution of 10-100 nm to be obtained.