Ion exchange chromatography is a method for protein purification which separates molecules by charge. The protein’s charge is a function of the molecule’s amino acid composition and the pH of the buffer relative to the molecule’s isoelectric point (pI). Ion exchange resin, or media, attracts the molecules based on their charge; molecules with a different charge, or no charge, pass through the media and are eliminated from the sample. Following the primary elution with a buffer change to alter the charge conditions allows the resin to release the protein of interest by exchanging it for another charged ion in the new buffer. Ion exchange is used in many analytical laboratories, and has many practical applications such as wine-making, desalination of water, preparation of drugs such as antibiotics and prevention of blood coagulation in stored samples. When choosing ion exchange media, consider the charge of the protein of interest, buffer conditions, resin pore size and binding capacity, and the loading capacity of the column. Research, and some trial and error, will result in the proper protocol for sharp peaks and quality separation.