This chapter summarises empirical information on the structure of water molecules bound to proteins. The focus is on structures solved by X-ray crystallography, although complementary techniques of obtaining solvent structure are discussed briefly and, when appropriate, particular examples are given. The coverage includes: methods by which solvent structure can be observed; knowledge derived from database analysis of large numbers of proteins; particular examples of groups of well studied protein structures; the contribution of protein models obtained at very high resolution to the understanding of solvent structure; and an analysis of water molecules as mediators of complex formation. Finally, a conclusion and a perspective is presented regarding the direction in which this information can lead in building a cohesive understanding of the roles played by solvent in the structural integrity and biological function of macromolecules.