Protein crystallization is the process of formation of a protein crystal. While some protein crystals have been observed in nature, protein crystallization is predominantly used for scientific or industrial purposes. Like many other types of molecules, proteins can be prompted to form crystals when the solution in which they are dissolved becomes supersaturated. Under these conditions, individual protein molecules can pack in a repeating array, held together by non-covalent interactions. These crystals can then be used in structural biology to study the molecular structure of the protein, or for various industrial or biotechnological purposes.