Photodynamic therapy (PDT) is a treatment using visible or near IR light for. activation of the photosensitizer in the presence of oxygen. It is used in therapy of various diseases including cancer. In PDT a combination of a photosensitising drug, visible light and oxygen causes a production of cytotoxic reactive oxygen species that have direct or indirect effect on tumour tissue. After administration of a photosensitizer we expose the diseased tissue to a light usually of a wavelength above 600 nm. Due to the low penetration of the light with this wavelength, PDT is appropriate for the therapy of skin tumours, while the therapy of other tumours depends on the optic fibres used for light delivery. Selective concentration of photosensitizers in tumour cells can be achieved by coupling of ligands, such as antibodies on the photosensitiser or on specific delivery systems loaded by the photosensitizer.