Undergraduate biochemistry courses cover what proteins do, as enzymes, receptors, hormones, motors or structural components. The much more interesting question is how can proteins achieve all these functions? Presented here is an overview of the methods used in such projects, their possible applications, and their limitations. Focusing on the biophysical chemistry of proteins, the text is accessible to those with a general background in chemistry, physics and mathematics, though a good understanding of protein structure and enzymology is required. The text may be used in courses of protein science, by students embarking on master- or PhD-thesis work in this area or by professionals who need a quick reminder about the essentials of a method.