The use of imaging techniques severely catalyzes the gain in knowledge about biological systems. This chapter discusses the current state of spatially resolved detection of singlet oxygen with focus on the direct detection via its infrared phosphorescence. The technical approaches of spatially resolved detection, scanning in contrast to wide-field imaging, are evaluated. Investigations on the microscopic scale of cellular and subcellular structures and on the macroscopic scale of tissue are covered, including their advantages and limitations. The step from in vitro to in vivo systems is of vital importance for the vision of using singlet-oxygen luminescence detection to evaluate the efficiency of photodynamic treatment. Therefore, particular attention is given to investigations on the macroscopic scale. The time-resolved luminescence detection is evaluated as an especially important technique, since it allows the discrimination of singlet oxygen and other luminescence sources and the investigation of singlet-oxygen interaction with its surroundings.