Keratin proteins are widespread in nature, being found in the nuclei and cytoplasm of almost all differentiated eukaryote cells. However, they are best known as the principal structural proteins in hair, wool and skin. Because of difficulties associated with their extraction from biological samples, high sequence homology and the presence of numerous post-translational modifications, they have been less well studied than other protein families. Thanks to the advent of modern proteomic techniques we now have available a good suite of tools to study this neglected family of proteins.