Bacterial protein toxins are highly specific, extremely potent, and highly efficient to translocate into the cytosol of the target cells. These inherent properties make them very good candidates for biotechnological and therapeutic applications. Targeted intracellular drug delivery is a highly promising therapeutic approach, particularly in cancer therapy. This novel therapeutic approach requires highly specific targeting mechanisms capable of passage through the cell membrane. Bacterial toxins have evolved naturally to specifically target cell subtypes and subcellular organelles via receptor binding. Additionally, these toxins penetrate the cell membrane efficiently through the membrane translocation process, therefore making them ideal vehicles to deliver therapeutic agents into the host cytosol.