With few exceptions, currently marketed drugs act on proteins and high-quality protein reagents are essential for drug discovery and development. Recombinant proteins may be used as drugs or used for vaccine development or used as antigens to create protective antibodies. Antibodies and antibody-derived proteins are becoming increasingly attractive as therapeutic drugs. In medicine, the study of pathological protein mutations often helps us to understand the molecular mechanisms behind a disease. In the technological field recombinant proteins are already well established in diverse industrial processes such as those involved in the production and development of laundry detergents, food, textiles, petroleum, pulp and paper. A substantial amount of research is currently focused on making proteins serve as catalysts in the development of more efficient and greener chemistry solutions. Material science has links to all the fields above. For basic research, there are many unsolved questions in how proteins fold, how they are modified, and how they have evolved to be such efficient chemical catalysts. To investigate basic properties and features of proteins, there is a huge demand for high quality protein samples in adequate amounts.