  This manuscript is the written form of three lectures delivered by David
Chandler at the International School of Physics "Enrico Fermi", Course CLXXVI -
"Complex materials in physics and biology", in Varenna, Italy in July 2010. It
describes the physical properties of water from a molecular perspective and how
these properties are reflected in the behaviors of water as a solvent. Theory
of hydrophobicity and solvation of ions are topics included in the discussion.
