Elastic proteins occur in a wide range of biological systems where they have evolved to fulfill precise biological roles. The best known include proteins in vertebrate muscles and connective tissues, such as titin, elastin, fibrillin and spider silks. Interest in elastomeric proteins is currently high for several reasons. Firstly, they have biological and medical significance, particularly in human disease. Secondly, the unusual properties of proteins such as spider silks provide opportunities to develop novel materials. Thirdly, the development of scanning probe microscopy makes it possible to study structures and biomechanical properties of these proteins at the single molecule level.