Nearly all synthetic steps in industrial chemical manufacturing end with crystallisation. This is because it is almost always the most efficient method to purify and isolate the material. While most chemists are proficient at coming up with a basic procedure, when it comes down to the fine details, often crystallisation is seen as a mysterious process and subject to factors beyond our control. Various quality issues may be important for the product: purity, residual solvents, filtration speed, polymorph, crystal habit, and particle size distribution. Steve Winter at Solitek explains how an in-depth understanding of the crystallisation process will help keep these issues under control.