In materials science (specifically crystallography), cocrystals are "solids that are crystalline, single-phase materials composed of two or more different molecular or ionic compounds generally in a stoichiometric ratio which are neither solvates nor simple salts."[1] A broader definition is that cocrystals "consist of two or more components that form a unique crystalline structure having unique properties." Several subclassifications of cocrystals exist.[2][3]
Cocrystals can encompass many types of compounds, including hydrates, solvates and clathrates, which represent the basic principle of host–guest chemistry. Hundreds of examples of cocrystallization are reported annually.