A variety of biomolecules, including nucleic acids, proteins, polysaccharides, and other soluble and insoluble low-molecular weight components, are present in living cells. These molecules occupy a significant fraction of the cellular volume (up to 40%), resulting in a highly crowded intracellular environment. This situation is referred to as molecular crowding. Although the thermodynamic stabilities of DNA structures are known to be altered in a crowded environment, less is known about the behavior of nucleic acids and their interactions with cations and water molecules under such conditions. This unit describes methods that can be used to quantitatively analyze the molecular crowding effects caused by cosolutes on the thermodynamic stability, hydration, and cation binding of nucleic acid structures.