We have written much here in this magazine about the different properties of water. Some of them, such as surface tension, are of importance to the ability of aquatic fauna to function in their given environment. For example, surface tension permits water skaters to skate on the surface of the water where its habitat is neither the water below the surface nor the air above. However, more than a purely physical phenomenon, osmosis is of importance for life itself, for no physical phenomenon has any greater importance in biology than does osmosis. Without osmosis neither animal cells nor plant cells could function. Not only this, osmosis also appears in many different guises in our everyday existence. So, what is this strange phenomenon?