Proteins are biochemical compounds consisting of one or more polypeptides. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. Protein purification is the process of isolating a few proteins from a complex mixture, such as a cell or a tissue. It is an important step for identifying functions, structures or interactions of the protein of interest. Protein Purification: Principles and Trends discusses several current and important issues related to protein purification.