Abstract: In contrast to the thylakoid cyclic electron transport around photosystem I, cyclic electron transport around photosystem II (CET-PSII) is a little studied process. The functional mechanisms of CET-PSII and methods of their study are discussed in the review. The position occupied by this process in the ensemble of the pathways of electron sink from photosystem II is discussed as well as the role of CET-PSII in regulating the ATP/NADPH ratio and participation of cytochrome b-559 in CET-PSII. In green leaves of higher plants, CET-PSII may be underestimated because of the limited possibilities of the standard methods most frequently used in photosynthesis study. In stomata guard cells of chlorophyll-deficient leaves, where the rate of non-cyclic electron transport is insufficient under blue light excitation, CET-PSII is of separate interest. A special attention should be paid to the photoacoustic methods of CET-PSII studies.