Salt tolerance is a complex phenomenon leading to ionic imbalance, osmotic stress, and excessive generation of reactive oxygen species (ROS). Halophytes developed a range of adaptations to tolerate disturbances in their redox homeostasis caused by high salinity alone or by its combination with other stresses. Osmoprotectants are universal molecules whose chemical structure allows them for making efficient osmotic adjustments and exerting antioxidant activity. Combining these two abilities, they become effective molecules that prevent membrane injury and stabilize proteins/enzymes under high concentrations of salts or other harmful solutes. Components of antioxidant systems together with some osmoprotectants act as ROS regulating networks. Selected compatible solutes (carbohydrates, polyols, amino acids, betaines, polyamines, phenols) (i) allow for balancing ROS level and redox status, (ii) are involved in ROSdependent signaling pathways, and (iii) activate the osmotic response network under salt stress. Osmolytes are also sources of carbon, nitrogen, sulfur, and energy for cells. Through the interaction with other biocompounds and/or their involvement in different metabolic pathways/metabolic loops, they can modulate metabolic homeostasis, especially under environmental stresses, and thus affect plant salt tolerance.