Cyclic electron transport around photosystem-I, and the associated cyclic photophosphorylation process in chloroplasts is enabled by two pathways, which depend on the PGR5 protein and the chloroplast NADH dehydrogenase-like complex, respectively. When both pathways are defective, photosynthesis and plant growth are significantly impaired. The pgr5 mutant of Arabidopsis is particularly sensitive to fluctuations in light intensity, which can lead to photodamage of photosystem-I. The lecture will discuss the molecular mechanism of the photoprotection of photosystem-I, afforded by this cyclic electron transport process.