Protein crystallization is the process of formation of a regular array of individual protein molecules stabilized by crystal contacts. If the crystal is sufficiently ordered, it will diffract.  Some proteins naturally form crystalline arrays, like aquaporin in the lens of the eye.
In the process of protein crystallization, proteins are dissolved in an aqueous environment and sample solution until they reach the supersaturated state. Different methods are used to reach that state such as vapor diffusion, microbatch, microdialysis, and free-interface diffusion. Developing protein crystals is a difficult process influenced by many factors, including pH, temperature, ionic strength in the crystallization solution, and even gravity. Once formed, these crystals can be used in structural biology to study the molecular structure of the protein, particularly for various industrial or medical purposes.