It is generally considered that light microscopes based on focusing optics (far-field microscopes) have reached their resolution limits. This consideration has lead to the development of electron, scanning probe and optical near-field microscopes. These microscopes, however, are restricted to investigations on the specimen surface or detrimental to the specimen. In contrast, far-field microscopes are able to provide images from the interior of intact transparent specimens, such as human cells. The purpose of the present project is to develope far-field fluorescence light microscopes with fundamentally improved resolution. The resolution can be improved by enlarging articially the total aperture of the microscope (4Pi-microscopy) or by including in the focusing process certain photophysical phenomena of the fluorophore, such as stimulated emission. The project is based on concepts introduced and published by the applicant. They have the potential of providing resolutions in the range of 30-150 nm.