Photodynamic therapy (PDT) is a method of the treatment of localized cancers, based on a photochemical reaction between a light-activated molecule or photosensitizer (PS), light, and molecular oxygen. Correct choice of PS is of fundamental importance for PDT efficacy. Despite numerous studies in this field, most known PS have some drawbacks, e.g. lack of specificity and aggregation in aqueous media. Consequently, the search for an ideal PS is essential for further development of PDT. Here we review classification and analyse main features of different generations of PS and describe the mechanisms of their action. Various methods of targeted delivery of PS to tumor cells are discussed. The advantages of PS nanoparticles with the effect of aggregation-induced emission (AIE) over the classic photosensitizers are presented. A possibility of practical application of such light-emitting structures in cancer phototherapy is shown. K e y w o r d s: photodynamic therapy (PDT), photosensitizer, aggregation-induced emission ABBrEVIATIONS AEMA -2-aminoethyl methacrylate ALA -5-aminolevulinic acid AlPc -aluminum-phthalocyanine chloride AlPcS4 -aluminium-phthalocyanine tetrasulphonated (Photosens) AlS2Pc -disulfonated phthalocyanine BDP -borondipyrromethene BHQ3 -black hole quencher3 BSA -bovine serum albumin c(rGDfc) -Arg-Gly-Asp-d-Phe-Cys cyclicpeptide crGD -cyclic arginine-glycine-aspartic acid DCF-DA -dichlorofluoresceindiacetate DMSO -Dimethylsulfoxide DPBA-TPE -(3,3'-(2,5-dimethoxy-1,4-phenylene)bis(2-(4bromophenyl)acrylonitrile)-tetraphenylethene DSPE-PEG-Mal -1,2-distearoyl-sn-glycero3-phosphoethanolamine-N-[maleimide(polyethylene glycol)] DTPEBBTD -Donor-tetraphenylethene-benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole) Fr/NIr -far-red/ near-infrared GFLG -Gly-Phe-Leu-Gly-peptide HPMA -N-(2-hydroxypropyl)methacrylamide m-THPP -meta-tetra(hydroxyphenyl)porphyrin (Foscan)