This thesis describes the development and construction of a time-resolved confocal laser-scanning microscope for ultrasensive fluorescence detection in solution and on surfaces. The system is capable of monitoring single molecules in liquids and on surfaces, capable of performing emission and/or polarization spectroscopy, time-resolved spectroscopy with picosecond temporal resolution, and fluorescence correlation spectroscopy with sub-microsecond temporal resolution. Moreover, it allows ultrafast scanning of surfaces thus allowing wavelength, polarization and lifetime imaging of immobilized molecules and samples. Thus, several novel theoretical concepts of single molecule spectroscopy could be experimentally realized and tested.