Bacteria have an important role in human and animal morbidity, and a great number of them have developed antibiotic resistance. In the past recent years a new way of dealing with this problem has been studied: photodynamic inactivation. This method is based on administration of a photosensitizing substance that fixes itself in the bacterial cell followed by exposure to a light source. In the experiments done by many researchers on photodynamic inactivation of bacteria, both coherent and non-coherent light sources were used. This article is a review of these light sources and of some experimental results obtained by different authors.