Multidrug-resistant bacteria (MDR), which have arisen mainly due to the widespread usage of antibiotics, offers important threats to public health. As a result, the World Health Organization (WHO) has been stimulating the development of novel antimicrobials. MDR includes gram-positive and gram-negative bacteria with different mechanisms of antibiotics inactivation, including lipopolysaccharides layers impermeable to antibiotics, efflux pumps and enzymatic degradation. Antibacterial photodynamic therapy (aPDT) has emerged as a promising strategy to treat bacterial infections, mainly because it is a multi-target therapy, avoiding bacterial resistance. aPDT uses a photosensitizer (PS) activated by visible or near-infrared light in oxygenated environments, generating reactive oxygen species (ROS), which can oxidize and inactivate any surrounding biomolecule. Here, we discussed the main oxidation mechanisms that are responsible to inactivate key macromolecules and to reach the multitarget strategy. We discussed the main aspects that improve the photodynamic efficiency such as the amount of photosensitizer upload and the target-specific concept, for the main classes of aPDT photosensitizers. In the last section of this chapter, we compared membrane target for prokaryotes with organelle target for eukaryotes.