Osmolytes are molecules with the function among others to align hydrostatic pressure between intracellular and extracellular spaces. Accumulation of osmolytes occurs in the cell in response to stress caused by pressure change, change in temperature, pH, and concentration of inorganic salts. Osmolytes can prevent native proteins denaturation and promote folding of unfolding proteins. Investigation of the osmolytes effect on these processes is essential for understanding the mechanisms of folding and functioning of proteins in vivo. A score of works, devoted to the effect of osmolytes on proteins, are not always consistent with each other. In this review an attempt was made to systemize available array of data on the subject and consider the problem of folding and stability of proteins in solutions in the presence of osmolytes from the single viewpoint.