It has been known for over 120 years that the specific nature of ions differentially influences the physical behavior of macromolecules in aqueous solutions. In fact, Franz Hofmeister demonstrated in the late 1880s that proteins can be salted into or out of solution by ions according to a recurring series. Subsequent work has shown that this same series holds for myriad physical phenomena. The underlying mechanisms by which this operates were poorly understood for the entire 20th Century, but the physical principles are just beginning to come into focus. Similarly, the mechanisms by which sugars, amino acids, urea, trimethylamine N-oxide and other osmolytes affect macromolecules are also poorly understood. This symposium will concentrate on the physical properties of ions an osmolytes in solution. Particular motifs of interest will include ion/osmolyte effects on protein folding, colloidal particle aggregation, and molecular arrangements at the air/water as well as the macromolecule/water interfaces. Both theoretical and experimental work will be presented.